Maximising the stable environment - covering aspects such as ventilation, flooring, bedding, lighting and the use of therapeutic tools for the stabled horse

Article by Adam Jackson

Horses stay in their stables for different durations based on their care, training regime, health status, and seasonal changes.  Ensuring your horse's comfort and well-being in their stable is crucial, as inadequately designed facilities can lead to injuries, health issues, and fire hazards. With horse welfare under the spotlight with the focus being on the keeping and protection of animals under the European Union review, there is no better time to look at how we can maximise the stable environment.

Ammonia

Ammonia is a serious irritant that can harm the respiratory tract and cause breathing difficulties.  Lower concentrations of ammonia can irritate a horse's upper respiratory tract, while higher levels may skip this area and lead to inflammation and fluid buildup in the lower lungs.  Ammonia triggers inflammation, which increases mucus production and disrupts the function of cilia in the respiratory tract, negatively impacting the immune response.  When cilia malfunction, dust and dirt can accumulate in a horse's lungs, causing health issues and decreased performance.

Monitoring ammonia levels in stables is crucial, as levels should ideally be below 10 ppm, and an odour of ammonia typically indicates levels are dangerously elevated at 20-30 ppm, which can harm horses' health.  

Bedding

Ammonia can be managed effectively through proper stable management in addition to ensuring good ventilation. To improve the absorption of urine and faeces and lower ammonia levels, add extra dry bedding in the areas of the stable where the horse often soils.  A recent study has shown that even with regular cleaning, elevated ammonia levels can remain near the floors.  Using a combination of highly absorbent bedding materials and an ammonia-neutralising product can help lower ammonia levels.

Bedding made of pine shavings is excellent at controlling the ammonia levels.  The pine oil in the shavings tends to inhibit the bacteria that converts urine into ammonia, thus keeping the ammonia levels low.  In addition, bedding that has strong shavings provide cushioning rather than compacting together.

Stable floor setups

The type of surface on which a horse stands for extended periods can significantly influence its comfort, movement quality, and overall soundness. Consequently, it is essential to invest time and resources in choosing the appropriate flooring for your stables. Moreover, selecting the right flooring can enhance operational efficiency and lower costs associated with hygiene management and stable cleaning. Finally, conduct routine inspections of your flooring to guarantee safety and avert potential hazards.

There are two main categories of flooring: permeable and impermeable.

Permeable or porous stable flooring can consist of either conventional packed clay or a specially engineered geotextile membrane. In the case of the latter, the membrane layers act as a barrier between the horse and bedding and the underlying base material. 

In both scenarios, it is essential to install pervious materials on a foundation of well-graded crushed and compacted stone.  There are disadvantages associated with the use of pervious flooring. While packed clay is softer than cement or asphalt, it is prone to becoming uneven when exposed to additional moisture, particularly if deep bedding is not utilised. 

Membrane layers can also contribute to urine accumulation, leading to an increase in ammonia levels that negatively impact the respiratory health of horses. Furthermore, this moisture can permeate the underlying base material, resulting in the development of unpleasant odours. Another significant issue with this type of stall construction is the potential for groundwater contamination.

Stable flooring that is impermeable or impervious is specifically engineered to stop urine and moisture from seeping through. To facilitate the elimination of urine and faeces, it is essential to either grant the horse access to an outdoor space or to supply bedding that can absorb moisture and offer cushioning.  

It is essential to have a solid foundation beneath for the entire system to function effectively. Stall flooring consists of a base layer and an upper layer of material. If the base is not properly established, the overall performance will be compromised. 

Additionally, rubber matting is regarded as an ideal durable choice due to its ability to mitigate hardness, alleviate fatigue in the horse's legs, and simplify the cleaning process. Rubber mats may require a significant initial investment; however, they offer long-term benefits by facilitating consistent cleaning, lowering bedding expenses, and enhancing the health, comfort, and overall wellbeing of horses.  

A correctly installed rubber mat should be even and stable while offering a degree of cushioning. The market offers a range of matting options, including custom wall-to-wall installations and interlocking mats. It may be beneficial to explore mats that are thicker and more cushioned to provide insulation against cold floors and to minimise the risk of pain in the hip, stifle, hock, fetlock, and pastern areas.  

In certain circumstances, it may be necessary to install a drain in a non-porous stall to facilitate the collection of liquids. A drain is particularly beneficial in veterinary or maternity stalls that require regular washing. Drains should be situated near a wall, and the stall should be graded appropriately. If drains are installed, ensure that cleanout traps are included to capture and eliminate solid waste.

Ventilation

Good ventilation in stables is essential for removing bad odours, improving indoor air quality and humidity, which supports horse health, while also controlling temperature and condensation to extend the building's lifespan.

Horses are obligate nasal-breathers and grazing posture hinder their ability to effectively clear dust and debris from their respiratory systems.  Prioritising good ventilation is essential for maintaining horses' health, as it mitigates the risks of respiratory diseases caused by airborne pollutants. Failure to minimise airborne particulate matter like mould, mildew, and dust-borne bacteria can lead to serious respiratory diseases, including asthma, allergic reactions and upper respiratory tract viral infections (i.e. herpes, influenza).  

Another source of moisture is the condensation that develops within the barn.  Inadequate ventilation, especially from closed doors during cold weather, can lead to increased moisture buildup indoors.  The horses themselves are a source of moisture and with the more horses kept in for longer periods, the more condensation that is generated. Therefore, it is vital to refresh the air inside the barn constantly to ensure the health and well-being of the animals.

Natural ventilation offers the most affordable solution with minimal initial investment, zero maintenance expenses, and no energy consumption.  However, a combination of natural and mechanical ventilation can enhance air quality and comfort in a stable block. 

Installing air inlets low and outlets high in the barn harnesses the natural tendency of warm air to rise, improving ventilation efficiency.  To optimise ventilation, high outlet vents should be installed at the roof's ridges, where warm air naturally accumulates. 

During winter, the barn doors may remain shut to retain heat, while strategically placed vents ensure adequate airflow, and in summer, windows and stable doors may be left open to promote ventilation and comfort.  Using horse body heat to warm a stable leads to very poor interior air quality due to inadequate ventilation and the accumulation of ammonia and other gases.  In a well-ventilated, unheated stable with good air quality, the air temperature typically stays within 0-5° C /  5-10° F of the outdoor temperature.

A well-designed mechanically ventilated barn allows for precise regulation of indoor air quality, surpassing the capabilities of a naturally ventilated barn.  Power ventilation systems in barns often incorporate exhaust fans and high-volume, low-speed units strategically placed in main aisles, barn ends, or between stables for optimal airflow.  Individual fans in stables or aisles primarily serve to disperse particulates and repel insects rather than provide significant cooling.

If you are designing a brand new stable, the steeper the pitch of the roof, the faster the stale air will exhaust through the top ridge vents. 

Vents and grates at the bottom of stable partitions help improve air circulation, effectively reducing ammonia fumes from urine.  Stabled doors should feature grated panels to ensure both security and proper ventilation.

Water Supply

A steady availability of clean, fresh water is crucial for preventing dehydration and colic.  You can provide water in your stable using either buckets or automatic drinking bowls, depending on your setup.

Automatic drinking bowls can be costly and require installation.  It's difficult to gauge your horse's water intake, but you can minimise physical labour in the yard and make sure your horse has constant access to fresh, clean water.

Water buckets are an affordable choice and you can track your horse's water intake, but it involves lifting and transporting the buckets to and from the stable.  

Lighting

Horses possess an internal timing mechanism known as a circadian rhythm, which regulates various physiological and behavioural functions.  This internal clock is controlled by the daily 24-hour cycle of light and darkness and operates in nearly every tissue and organ.  

Scientific research supports the use of lighting systems that emit blue light similar to sunlight is advised for daytime use and a soft red light should be utilised during the night.  Enhancing stable lighting can optimise the horse's health and wellbeing by supporting its natural circadian rhythm.  All elements of their physiology can function more harmoniously and in sync with the environment.

Social interactions 

Recent studies indicate that private stables may not promote health and well-being as effectively as communal environments.  The results indicated that horses housed in 'parcours' exhibited minimal abnormal behaviours like stereotypies, had the freedom to move throughout most of the day, engaged with other horses, and maintained positive interactions with humans.  

Although this may not always be viable within training yards, stable adaptations can be made to increase social interactions. Windows in stables with views to other stables or paddocks allow horses to see and interact, even if they are not in direct contact, stall partitions with bars allow for visual and olfactory contact and individual turnout paddocks or pens allow horses to graze and interact in close proximity.  

Feeding and entertainment

Horses should ideally have unrestricted access to hay; however, using slow feeders or automated feeders are also available to provide small portions throughout the day.

Entertainment devices can also help stimulate interaction and engagement, reducing the chances of stress and the emergence of negative habits (vices).  Stable toys, mineral licks, stable treats, spreading forage in different locations, visual stimulation such as mirrors and brushes affixed to walls or fences all offer enrichment.

Technology

A range of technology is increasingly accessible to facilitate continuous care around the clock.  Technology has the potential to staff, allowing them to redirect their time towards enhancing equine welfare.

The integration of camera-GPS surveillance with specialised software monitors the movements of individuals and determines the typical behaviour patterns for each horse within the herd.  This cost-effective technology can alert yard personnel if a horse exhibits unusual behaviour.

There are a range of therapeutic technologies that can be utilised in the stable environment such as massage rugs, leg wraps and boots and handheld complimentary devices; as well as additional training and rehabilitation systems such as spas, treadmills, combi floors and solariums. All of which can be considered for enhancing the horse's well-being. 

Conclusion

Ensuring the comfort and well-being of the horse within the stabled environment by adapting structures and utilising enrichment tools can help prevent injuries, health issues and fire risks. By promoting best practice for keeping the competition horse and ensuring natural behaviours are expressed as much as possible within the training regimes, will only benefit the horse thus increasing performance results.  

Spring allergies - how to treat spring allergies and the effects they have on the respiratory tract

Article by Becky Windell

Spring allergies – peak season of the year-round battle

As obligate nasal breathers horses are predisposed to inhaling respirable dust, mould, pollen and other irritants from the environment. Whilst they have defence mechanisms to deal with it, the horse can be overloaded with the amount they are exposed to. 

Springtime brings an array of newfound pollen from trees, grasses, and crops including the infamous oilseed rape (OSR). This pollen offensive comes in addition to the other allergens in the horse’s environment often surpassing the threshold of irritant load. This can result in respiratory based “spring allergies” with inflammation in the airways leading to allergen based equine asthma. Either subtle signs such as poor performance and reduced stamina will appear and/or more obvious clinical signs such as coughing and nasal discharge1. Horses will tire early due to the reduced amount of oxygen being taken up by the blood from the lungs.

Plants are polyploids and show many gene duplications so cross reactivity among species in which different antigens appear similar to the immune system can amplify the horse’s response to pollen and is particularly the case for grass pollens.2

Generally intact pollen grains range from 10–100 μm in size, this is bigger than respirable particles which are classified respirable at <5 μm. Therefore, pollen has not generally been implicated in Equine Asthma and tends to be considered more of an irritant than allergen. However, a study by White et al identified an association with pollen in a group of horses with Severe Equine Asthma (SEA) while looking at bronchoalveolar lavage fluid (BALF) samples compared to healthy horses2. The effects of pollen on the horse is an area where more research is needed.

Oilseed rape on the decline

It’s well documented that oilseed rape (OSR) is a concern for trainers with some experiencing underperforming horses while surrounding fields are flowering oilseed rape crops. 

Whilst it’s still unclear if there’s truly an allergic component to it, it certainly seems to irritate a lot of horses and vets see pollen in the tracheal washes when OSR is in flower. 

A study in people comparing spring allergy symptoms of people living near OSR and those living far away, found small but significant excesses of cough, wheeze, and headaches in spring in the oilseed rape area3. Interestingly they also found counts of fungal spores were mostly higher in the rape than the non-rape areas so perhaps pollen is not the culprit but fungal spores on the crop…?

This is worth noting as fungi is proven to cause respiratory problems in horses. A study by Dauvillier et al found horses with fungal elements observed on the tracheal wash (TW) cytology had 2 times greater chance of having equine asthma than horses without fungi4. They also found the risk of being diagnosed and likelihood of fungi in TW were higher when horses were bedded on straw or fed dry hay which are key sources of fungi in the horse’s environment.

Practical solutions to OSR have been for trainers to purchase neighbouring fields or pay their neighbouring farmer not to grow the OSR.

From the farmer’s perspective OSR has been an essential part of the arable crop rotation for many years now. It is a crop specially planted to give the cereal crops a ‘break’ from the cycle of weeds, pests and disease that build up in the soil. This helps to improve the yield of the crops that are grown afterwards, such as wheat. 

It used to be good for removing grass weeds too but has become less useful for this purpose in recent years due to weed resistance. In fact, a number of previously positive reasons to grow OSR are no longer standing up. A flea beetle which previously could be treated with a neonicitinoid is no longer licenced for this use, soil borne diseases have become a problem, and the crop does not do well in the wetter winters. 

Ultimately it is now less profitable. This is good news for trainers with farmers starting to use the crop less often and perhaps grow it every 6th year rather than ever 3rd year in a field. Its use is on the decline in UK/Ire and this can been seen in government figures, in 2023-24 all regions in England saw decreases in the oilseed rape area with the largest proportional decrease seen in the North East and the overall decrease of OSR grown in the UK of 27%.5 While in Ireland Winter oilseed rape declined by 30% in 20246. 

Now the interesting question in time is how much will the incidence of spring allergies reduce with the reduction in oil seed rape? 

Global Warming

Dr. Emmanuelle Van Erck Westergren, founder of Equine Sports Medicine Practice in Belgium cautions about the effects of global warming on seasonal allergies. Global warming is altering fungal behaviour and distribution, offering conditions that provide opportunities for fungi such as Apergillus and increases the risk of mycotoxins. In addition the burden of pollen is increased by warming temperatures.

Diagnosing spring allergies

Regular, routine tracheal washes (TW) are useful as a quick and easy “screening” procedure. They help monitor how inflamed the airways are by looking at the neutrophils and macrophage cells. Normal samples are typically of low to moderate numbers of nucleated cells, the nucleated cells being mostly macrophages, with <10% neutrophils. An elevated proportion of neutrophils in the TW is considered to indicate airway inflammation, and cutoff values for neutrophil percentage have been set at 20% for TW.

Ian Beamish partner at Baker McVeigh Lambourn equine practice says he uses the tracheal wash to see “how the army is looking” in terms of number of cells and how many of those cells are dying on the battlefield. 

He also warned “Ultimately, it can be a struggle to determine the actual cause of inflammation of the airways. Whilst spring allergies is a strong possibility at this time of year it could be any number of allergens from the environment causing it or simply the addition of more burdening the system. And then it could also be a virus! It’s important to remember racehorses are immune suppressed from being in full training so they are susceptible to low grade viral disease which can present with similar poor performance.”

To establish if the horse is truly allergic or if it is simply an irritation of the airways there is a diagnostic blood test for allergens. Measuring allergen-specific IgE antibodies present in the serum, can help to identify environmental allergens for both allergen avoidance purposes and to select for inclusion in allergen-specific immunotherapy (ASIT). This can be a helpful aid for diagnosing allergic disease but has been known to give occasional false positives so cannot be relied upon. Establishing the specific allergy is unfortunately very difficult.

Performance Horse Consultant and highly experienced equine vet Peter ‘Spike’ Milligan advises to first and foremost control what you can.

“Reducing contact with pollen can be extremely challenging so first focus on what you can control.  Irrespective of the time of year, regularly re-evaluate the stable environment as well as the forage and bedding quality. This includes how they are stored, prepared and used to ensure the allergen and irritant load is as low as possible.”

A useful tool

The pollen count measures the number of pollen grains in a given volume of air and can indicate if it is a day the horse will be exposed to high concentrations of pollen. Pollen count is affected by the season, weather and even the time of day. The largest concentrations of pollen are found on days of high radiation and wind, early in the morning when pollen is first shed when the air is warming and rising and in the evening as the pollen in the air descends to nose level with the afternoon air-cooling. 

The pollen count can be checked daily on weather apps. Where possible, it’s advisable to adapt the horses training schedule in line with the pollen count and keep training sessions less strenuous on the days the pollen count is high.

Treating spring allergies

Treatment of horses with allergen-induced equine asthma focuses mainly on decreasing and controlling airway inflammation1. The standard and effective cornerstone treatment is to give a systemic or inhaled corticosteroid and if necessary, a bronchodilator can also be used. 

The preferred method to administer these tends to be via a nebuliser because inhaled therapy delivers the drug directly to the lungs and helps to loosen mucous. In addition, a lower dose can be used reducing the chance of side effects and shortening the drug withdrawal time required prior to racing.

Recent advances in treatment include a specifically designed inhaler with a different inhaled steroid, ciclesonide, studies have demonstrated improved clinical signs in a group of horses with mild to severe equine asthma.7,8

However, whilst corticosteroids are very effective and efficient at relieving airway obstruction, they have limited residual effect after treatment stops and long‐term administration is usually limited due to the risk of laminitis, immunosuppression, and interactions with endocrine metabolism9. The drug withdrawal period also impacts the racing schedule. So, what treatments can be used which interfere less with their training and racing plan?

Firstly, creating a barrier between the horse’s airways and the pollen with Nostrilvet or similar and/or the use of a nose-net are low-cost options for training that could be worth a try. This could help to reduce the irritant load on non-race days.

If the horse is truly allergic to certain pollens, then de-sensitisation injections can be used with no withdrawl period necessary. Known as allergen-specific immunotherapy (ASIT) it is a safe long-term treatment which has been used successfully for allergen-induced Equine Asthma. The efficacy of the treatment can vary however, studies suggest that approximately 75% of cases treated showed a good response, with either no need or a reduced need for steroids.

Immunotherapy aims to make the horse tolerant to the environmental allergens that have been diagnosed as responsible for their clinical signs by introducing increasing amounts of the allergen to which they are sensitive. These desensitisation vaccines are administered to the horse subcutaneously. The initial treatment lasts for approximately 10 months, with a dosage regime that gradually increases until the maximum tolerated dose is reached. This is then followed by maintenance treatment. The length of time for a response has been reported to vary between individual horses and can be anywhere from 4 and 12 months. Treatment can be ongoing as premature discontinuation may result in the clinical signs recurring.

Developments in orthobiologics has brought a new non-corticosteroid anti-inflammatory alternative for use in affected horses. Alpha-2-macroglobulin (α2M) is a naturally occurring protein within the blood and is the horses natural defence against inflammation10. Plasma proteins are filtered from the horse’s own blood, leaving an isolated, concentrated alpha-2-macroglobulin product which can be nebulised using a Flexineb. It’s high-priced and still early days for this product but offers a potential drug-free way to treat. It is also an effective anti-inflammatory in joint disease.

Principally the greatest threat to respiratory health year-round is from environmental sources which you can control – the forage, the bedding and the overall stable hygiene environment, this should never be overlooked.

References

1. Couetil L, Cardwell J, Garber V, et al. Inflammatory airway disease of horses— Revised consensus statement. J Vet Intern Med 2016;30:503-515

2. White S, Moore-Colyer M, Marti E, Coüetil L, Hannant D, Richard EA, Alcocer M. Development of a comprehensive protein microarray for immunoglobulin E profiling in horses with severe asthma. J Vet Intern Med. 2019 Sep;33(5):2327-2335. doi: 10.1111/jvim.15564. Epub 2019 Aug 20. PMID: 31429513; PMCID: PMC6766494.

3. Soutar A, Harker C, Seaton A, Brooke M, Marr I. Oilseed rape and seasonal symptoms: epidemiological and environmental studies. Thorax. 1994 Apr;49(4):352-6. doi: 10.1136/thx.49.4.352. PMID: 8202906; PMCID: PMC475369.

4. Dauvillier J, Ter Woort F, van Erck-Westergren E. Fungi in respiratory samples of horses with inflammatory airway disease. J Vet Intern Med. 2019 Mar;33(2):968-975. doi: 10.1111/jvim.15397. Epub 2018 Dec 21. PMID: 30576012; PMCID: PMC6430897.

5. Gov.uk website - Accredited official statistics Cereal and oilseed areas in England at 1 June 2024. Updated 29 August 2024 https://www.gov.uk/government/statistics/cereal-and-oilseed-rape-areas-in-england/cereal-and-oilseed-rape-areas-in-england-at-1-june-2023#:~:text=1.7%20Oilseed%20crops,244%20thousand%20hectares%20in%202024.

6. Teagasc Crop Report www.teagasccropreport.ie Harvest report 2024. https://teagasccropreport.ie/reports/harvest-report-2024#:~:text=The%20area%20of%20winter%20oilseed,of%2021%2C600%20ha%20in%202023.

7. Lavoie J, Bullone M, Rodrigues N, et al. Effect of different doses of inhaled ciclesonide on lung function, clinical signs related to airflow limitation and serum cortisol levels in horses with experimentally induced mild to severe airway obstruction. Equine Vet J 2019;51:779-786.

8. Ciclesonide [prescribing information] Duluth, GA: Boehringer Ingelheim Animal Health USA Inc. 2020.

9. Mainguy-Seers S, Lavoie JP. Glucocorticoid treatment in horses with asthma: A narrative review. J Vet Intern Med. 2021 Jul;35(4):2045-2057. doi: 10.1111/jvim.16189. Epub 2021 Jun 3. PMID: 34085342; PMCID: PMC8295667.

10. Alpha-2 Macroglobulin for the Management of Equine Asthma Summary Results of a Pilot Study Dan Dreyfuss, DVM

Addressing drug resistance in equine tapeworms

Article by Jacqui Matthews

Tapeworms are important parasites of horses

All horses can be infected with internal parasitic worms, which can cause health issues, including weight loss, diarrhoea, and colic. The most common worms affecting racehorses, and other horses, are the small strongyles (cyathostomins) and the common equine tapeworm, Anoplocephala perfoliata. Horses are infected by ingesting parasites from contaminated grazing, whether it be a field, turn-out paddock or opportunistic grazing on training grounds or racetracks. 

Recent reports of dewormer resistance in A. perfoliata are very concerning, especially as there are few available products to treat these parasites and no new drugs are expected to enter the market soon. These relatively large parasites typically reside at the junction of the small and large intestines and can cause colic. The worms attach in clusters to the intestinal wall, which can cause mechanical obstruction and mucosal damage. 

Blockages can cause impaction, potentially necessitating surgery. Moreover, the presence of tapeworms may lead to intussusception, where one segment of the intestine telescopes into an adjacent segment, also requiring surgery. Studies indicate that having as little as 20 tapeworms can cause significant damage to the intestinal wall (Pavone et al. 2010). Therefore, it is crucial to prevent such burdens from accumulating in horses.

Tapeworm resistance to deworming products 

There are two types of dewormers (anthelmintics) available for treating tapeworms: praziquantel and pyrantel (given at double the dose used for treating roundworms). In the UK and EU, there have been several anecdotal reports of reduced effectiveness of anti-tapeworm drugs. A recent research study on a Thoroughbred farm in the US evaluated the performance of both tapeworm dewormers (Nielsen, 2023). 

The results demonstrated treatment failures in foals and broodmares in which tapeworms survived treatment. This was the first formal report of suspected drug resistance in tapeworms. Resistance occurs when parasites survive deworming treatments and pass on reduced sensitivity to the drugs to subsequent generations. Repeated treatments with the same drug can lead to parasite burdens that cannot be cleared and may result in clinical disease. 

Given the threat of resistance in this species, it is essential to reduce the overuse of anti-tapeworm medications. Implementing more sustainable control methods is now crucial for the long-term effectiveness of these important dewormers. These control methods must include:

• maintaining a clean grazing environment 

• regularly monitoring parasite burdens 

• deworming only those horses that truly need treatment. 

Use grazing management methods to reduce reliance on dewormers

Tapeworms differ from other common equine worms because they develop inside mite intermediate hosts on paddocks (Fig. 1). Horses become infected when they consume hay or grass that contains tapeworm-infected mites. Mites are infected by eating eggs passed in the dung of infected horses.  Where horses have access to grazing paddocks, it is essential to remove dung daily and dispose of it well away from both the grazing area and any water sources. Extra caution should be taken with horses that have grazed away from the yard and newcomers to the yard (see quarantine recommendations below).

Use tests to reduce dewormer treatment frequency

Regular testing is essential for effectively managing tapeworm infections. Faecal egg count (FEC) tests are unsuitable for detecting tapeworms. These detect worm eggs shed in dung, but are not reliable indicators of the overall parasite burden in individuals, particularly since immature worms are not detected. FEC methods are also influenced by the variable release of egg-containing segments from adult tapeworms. 

The main purpose of FEC tests in tapeworm control is to assess the effectiveness of deworming treatments. If tapeworm eggs are detected in dung samples taken two weeks after treatment, this is a significant finding. However, the absence of eggs in a FEC does not mean that tapeworms are not present. If resistance is suspected, this should be discussed with a veterinary surgeon. 

Tests that measure antibodies to tapeworm provide valuable information about levels of infection and should be used to guide treatment decisions. Antibody tests are available in blood and saliva formats. In the blood test, samples are collected by a veterinary surgeon and sent to the laboratory for analysis. 

This test measures levels of tapeworm-specific antibodies in the blood, with results reported back to the veterinary surgeon as "serum scores." These scores are categorised as low, borderline, or moderate/high, and treatment is recommended for horses with results in the borderline or moderate/high categories.  The non-invasive saliva test involves taking a sample from the horse’s mouth using a specially developed swab (Fig. 3) and does not require a veterinary surgeon. 

The swab containing the saliva sample is mailed to the laboratory in a preservative solution, ensuring stability for at least three weeks. At the laboratory, the saliva sample is assessed using a special three-ELISA system that accurately measures tapeworm-specific antibodies, with the results reported as “saliva scores”. Similar to the blood test, the saliva test categorises results as low, borderline, or moderate/high, with treatment recommended for horses that have results in the second two categories. Because antibodies take time to decrease after effective treatment, horses should not be tested again until 4 months after the last deworming for blood tests or 3 months for saliva tests.

By reliably detecting tapeworm burdens, antibody tests enable treatments to be targeted to only those horses that need treating and therefore reduce the risk of dewormer resistance. Results from tapeworm testing have led to significant reductions in the use of dewormers; from 2015 to 2022, over 164,000 horses in the UK were assessed using the saliva test, with only one-third recommended for treatment (Matthews et al. 2024). 

Applying tapeworm testing at racing yards

Tapeworm testing frequency can be determined by conducting a risk assessment. Key risk factors include age and access to contaminated grass, as well as historical test results. These parasites can be long-lived and persist for extended periods, so it is essential to consider each horse’s history during or before training. 

While most horses in training are at low risk due to having limited pasture access, yearlings and two-year-olds may have higher burdens, especially if from breeding farms or other premises where there is a high level of infection. However, all ages of horses are susceptible to tapeworms. Regular assessments with a veterinary surgeon will also identify risk factors in yard management practices, including those associated with activities like short daily turnouts. A comprehensive risk assessment will:

1. Identify which tests to perform (FEC tests, small redworm blood tests, tapeworm tests) and the frequency of testing

2. Highlight the need for treatments for high-risk horses when tests do not provide information for treatment decisions

3. Provide information on worm exposure and ways to minimise infection risks.

If significant risks are detected, such as a high level of tapeworm infection indicated by testing or the frequent introduction of new horses, testing should occur every six months. Once a year testing may be appropriate in low-risk situations where previous testing has shown low evidence of tapeworm infection. 

Testing identifies infected horses that could spread infection to others, allowing for prompt treatment and reducing the risk of colic. If many horses test positive, it is crucial to identify the source of infection and improve management practices to reduce spread. In a recent case study on a UK training yard, 56 horses were tested for tapeworm antibodies. 

The results revealed that only 14% of the horses had tapeworm burdens that required treatment. These horses were turned out in a small paddock for just 30 minutes each day, and because dung was not removed from the area, the paddock was identified as a source of infection. The trainer was advised to remove the dung from the paddock daily and to treat any horses that tested positive for tapeworms. 

This testing protocol not only helped reduce the overall deworming frequency, but also provided the trainer with valuable information about horses at risk of colic. It also highlighted potential areas for improving parasite management practices.

Avoiding the introduction of new or resistant worms

Introducing new horses to racing yards requires proper assessment to determine if they have roundworm (small redworm, ascarid) or tapeworm infections. The traditional method of treating all newcomers with a broad-spectrum dewormer is outdated and should be avoided due to increasing drug resistance in all common parasites. Instead, it is recommended to assess new horses using appropriate tests, specifically;

1. FEC tests to identify if they are shedding eggs such as small redworm and ascarid eggs 

2. Blood tests to detect small redworm stages that may not be detected using FEC tests

3. Tapeworm tests to identify horses that need specific treatment for this parasite. 

If any of these tests return positive results, the appropriate dewormer can be selected to target the parasites present. Furthermore, if a horse tests positive in the initial FEC test, it is advisable to conduct a follow-up FEC test two weeks after treatment to determine whether the dewormer has been effective.

In conclusion

Every horse will encounter parasitic worms at some point in their life, making effective parasite control essential for their health and well-being. While traditional all-group dewormer treatments have been common, rising cases of dewormer resistance reveal that this approach is no longer sustainable, especially as no new anti-tapeworm treatments are expected soon. 

Using tapeworm tests to determine if treatment is needed is crucial to maintain the effectiveness of existing dewormers. Many horses in low-risk environments have minimal or no tapeworm infections, making regular treatments unnecessary. Testing helps identify only those horses that truly need treatment, thus promoting the longer-term efficacy of dewormers. 

In the racing industry, there is significant overuse of dewormers, with few trainers using evidence-based practices. It is essential that the spread of resistant worms is prevented, especially as racehorses move to various environments (breeding farms, sport horse yards, sanctuaries, leisure horse premises) where more vulnerable horses may reside. For this reason, the industry must adopt management-based and test-led methods to control worm populations effectively.

References

Matthews et al. 2024. In Practice 46:34-41.

Nielsen. 2023. Int J Parasitol Drugs Drug Resist. 22, 96-101.

Pavone et al. 2010. Vet. Res. Commun. 34, S53-6.

Exercise associated sudden death - improvements to equine safety and welfare to reduce incidences

Article by Celia Marr

In racehorses, exercise-associated sudden death – or EASD – is a very rare event but, the miserable events at Cheltenham last November where three horses died on the same day, drew considerable negative attention to the condition and highlight a need for better understanding of why it happens as well as motivating vets, researchers and horsemen to do more to prevent it. 

Cheltenham drew a spotlight to the problem but EASD was already the focus of international effort: in June 2024, Woodbine Racecourse, Toronto hosted the International Horseracing Federation’s (IFHA) Global Summit on Equine Safety and Technology where EASD was one of two major workshop topics. This international event was sponsored by Cornell University’s Harry M. Zweig Memorial Fund for Equine Research, The Hong Kong Jockey Club Equine Welfare Research Foundation, and Woodbine Entertainment Group and specialist veterinary clinicians, pathologists and researchers spent two days sharing knowledge and ideas and debating how tangible improvements to equine safety and welfare in racing could be made towards reducing the prevalence of both EASD incidents and severe musculoskeletal conditions.

What is EASD?

The term EASD is used to describe a fatal collapse in a previously healthy horse either during or shortly after exercise. Currently, across the world, different time-windows are used by regulators which makes quantification of the problem challenging. A  benchmark definition is needed so that the occurrence rates can be audited and the EASD workshop team advised that an international definition is adopted to define EASD as within approximately one hour after exercise. Figures from the BHA show that in the UK, the 2024 EASD incident rate was 0.04% or 4 horses per 10,000 starts – which with just under 90,000 runners translates to 36 EASD losses for the year which is why the triple Cheltenham deaths were so extraordinary. The UK’s rate is comparable with other nations such as Australia and a little lower than the USA although the different definitions used in different racing jurisdictions make direct comparisons challenging. 

Four broad EASD categories

The most authoritative international study looking at causes of EASD was performed with the Horserace Betting Levy Board supported by a group in the University of Edinburgh’s Royal Dick School of Veterinary Studies. This report showed that determination of cause of death is significantly impacted by individual pathologist’s interpretation of findings, however, in broad terms about a quarter of cases EASD have a clear and definitive diagnosis of cardiopulmonary failure and a further 10-15% have necropsy findings which are strongly suspicious of cardiac or pulmonary failure; around 10% of EASD cases are due haemorrhagic shock brought on by rupture of a major blood vessel which is most commonly within the abdomen,  while unfortunately around 20% of cases are unexplained despite detailed examination. A range of other rare conditions including brain and spinal problems, often relating to trauma, account for the remainder. 

Within the cardiopulmonary failure category, it is generally accepted that the majority relate to cardiac arrest. This means that the cardiac rhythm is disrupted but, in fact it is actually very difficult to prove that a cardiac rhythm disturbance has been the trigger mechanism of death during a post-mortem examination. In the June 2024 IFHA summit, a significant amount of the workshop was dedicated to discussing current knowledge of cardiac rhythm disturbances, why they occur and how they might be detected in future.

Cardiac arrest: a “perfect storm”

Cardiac arrest can be likened to a perfect storm where multiple adverse factors combine with devastating impact. Unlike catastrophic bone fractures or tendon injuries, cardiac arrest does not necessarily relate to an accumulating pathway of built-up microdamage and because of this, it is very difficult to predict cardiac arrest might occur.  For a cardiac rhythm disturbance (aka an arrhythmia) to develop three elements are required: a substrate, triggers and, in some cases, one or more modulators.  A substrate refers to the structure of the heart, this can be an area of scar tissue but the heart structure does not necessarily need to be pathological and the changes in muscle content which arise as a result of athletic training may also be a substrate. 

A trigger reflects a change in the cellular and tissue environment such as alteration in concentrations of different electrolytes or development of low oxygen concentrations in the tissues yet changes in electrolytes and lowering oxygen concentrations occur every time a horse gallops.  Modulators are an electrophysiological characteristic of the heart  which might be a permanent feature of an individual’s cell make-up or more often might be a transient state such as a variation in the nervous system brought on by excitement, stress or perhaps pain. 

The key point is all these independent factors have to combine to precipitate a cardiac arrest – indeed a horse might go through its life uneventfully despite the presence of a particular substrate or it may experience these triggers on a daily basis and come to no harm. It is the coalescing of multiple factors at a given moment that precipitates the rhythm disturbance that leads to cardiac arrest. 

EASD at the molecular level

Arguably the biggest challenge we currently face in this arena is lack of knowledge of what is normal in the exercising horse. There is very little understanding of structural and electrical remodelling of the equine heart in response to exercise. We do know that the heart, just like any other muscle, will increase in size in response to training and we also know that in horses competing over longer distances such as steeplechasers, a big heart confers an athletic advantage. Exercise training can also lead to scar-tissue formation but in both human and equine athletes the importance of this pathology is uncertain. There is some evidence that fit horses also have altered cardiac electrical characteristics but again, knowledge in this field is very sparse.

Electrical activity in the heart muscle cells is controlled by ion channels – these are proteins that are sited within the cell membranes which effectively act as gates opening and closing to allow electrolytes such as sodium, potassium and calcium to move in and out of the cell and in doing so the electrolytes carry the electrical current. 

Channelopathies – or abnormalities in these ion channels  - have an important role in the development of rhythm disturbances but right now, research on equine ion channels has been limited…but that is changing rapidly.  Researchers in Surrey, Copenhagen and various US universities are working to understand equine channels and the genetic and acquired factors that determine how they function. As knowledge accumulates it may be possible to include tests for the molecular make -up of an affected individual in post-mortem exams – the so-called “molecular autopsy” which is improving diagnosis rates in human cardiac arrest suffers.

So far equine studies have not found conclusive evidence of genetic mutations associated with EASD. But there is evidence for heritability in the Thoroughbred: observations from Australia which have shown some stallions’ and at least one mare’s progeny have higher rates of EASD associations suggesting that it is likely that there are genetic elements at play in EASD. One of the key recommendations of the IFHA’s EASD workshop was that tissues from both horses impacted by EASD and those dying of other causes should be banked and shared amongst researchers to underpin and promote research studies in this area. 

ECG is the cornerstone of arrhythmia diagnosis.

Currently vets rely on resting and exercising electrocardiograms (ECG’s) to identify horses with arrhythmias. However, there are a number of limitations to using ECG as a screening and diagnostic tool: 

• ECGs can be technically difficult to perform during exercise as they are affected by motion artefact; leading to reduced quality of the trace. 

• ECGs currently must be manually interpreted, which is time consuming and leads to significant intra- and inter-observer variability.

• There are no universal guidelines on how to perform the ECG; i.e. exactly where to place the electrodes, which affects the trace produced. 

• There is no consensus on interpretation of the results of an ECG examination in terms of the clinical significance of any abnormalities detected and whether the clinical presentation impacts criteria for interpretation. Indeed, we need to understand more about what is ‘normal’, before we can identify horses with an ‘abnormal’ trace.

Will wearables change the diagnostic landscape?

Over recent years, increasingly racehorse trainers have been using wearable devices during routine training. Generally, the trainer’s motivation is to collect data on speed and fitness variables in their horses to refine their training programmes but several of these devices also have the capacity to include an ECG trace. The ECG can then be accessed if the horse has a problem during a training session and, usefully, the horse’s past record can also often be interrogated. The large numbers of recordings that are currently being made represents an untapped resource for collecting ECG information from large numbers of horses to better understand cardiac responses during exercise in both healthy and unhealthy individuals. 

It has been known for some time that healthy horses frequently have mild rhythm irregularities – generally described as premature complexes or premature depolarisations – these minor fluctuations in rhythm occur at all phases of exercise and particularly as their heart rate is slowing rapidly at the end of a gallop. But the dividing line between what is normal variation and what is clinically concerning is not clear-cut. We do not know exactly how much beat-to-beat variation can be classed as normal versus a sign of significant arrhythmia and we have little understanding of the relationship between premature depolarisations and other factors such as stress, exercise intensity, medical interventions and adverse clinical events.

As a result, veterinary clinicians are looking forward to the ongoing expansion of wearables as an exciting new window into equine cardiac function. Yet, the scale of the unexplored data collection currently going on in training brings with it a challenge – with so many ECG traces being rapidly collected, how can we address the mammoth task of actually looking at them? Artificial intelligence (AI) is revolutionising many aspects of modern life, including medical diagnosis. There is an urgent need to develop AI systems which can screen training ECGs to identify those that warrant further attention. And, although a large number of wearable devices are available on the commercial market, these products often lack validation which is needed before we can use the data they collect to make clinical decisions on individual animals and use the data as a research resource. 

Could we deal with EASD cases better when they do occur?

Racetrack arrhythmia/collapse are, in reality, low probability but high impact events which can be difficult to manage due to their traumatic nature and the fact that they are often played out in the public eye. This is compounded by the availability of medical equipment and limited treatment options that may be futile. 

However, when these events do unfortunately occur, they represent a golden opportunity to collect diagnostic information and biological samples which could be used to prevent future EASD events in other horses in the future.  The combination of an ECG history, a video of the horse as it suffers the event, information from necropsy if the horse dies, and tissue banking offers valuable research insights.

The nearest parallel event from human sport is the cardiac arrests which are occasionally seen in footballers. Through the effort of football’s regulators, today pitch-side emergency medical facilities are excellent and large numbers of trained staff are in attendance, all leading to the best possible outcomes for sportsmen when medical problems arise. When looking to perform cardiopulmonary resuscitation and treatment attempts in the collapsed horse, the animals’ size is a major challenge; human defibrillators simply do not work in large animals.  

We need more information on emergency medications that can be used in the presence of arrhythmias of unknown origin. These drugs need to be quick to administer, available and suitable to be carried by a racecourse vet, safe, effective and affordable. The IFHA’s EASD group identified that in pressurised situations, pre-determined protocol approaches to both emergency treatment and necropsy procedures are invaluable and the group is working to develop these protocols for dissemination across racing jurisdictions.

Will EASD risk always be present?

As EASD is such a rare event, it is impossible to believe that the risk of EASD can ever be removed entirely, but given the recent technological development in both veterinary science and wearables for training, there is reason to be optimistic that in the coming years, we will at last be able to improve diagnosis rates, identify some of the contributing risk factors and even potentially provide more effective emergency treatment options for these unusual but tragic episodes in our horses.

Is SDFT tendinopathy a “professional condition” in the jumping racehorse?

Words - Jean Baptiste Pavard

Tendon and ligament disorders are one major cause of poor performance and wastage in equine athletes. The most common structures involved are the superficial digital flexor tendon (SDFT), the suspensory ligament (SL), the deep digital flexor tendon (DDFT) and the accessory ligament of the deep digital flexor tendon (ALDDFT), also called the inferior check ligament.

Thoroughbred racehorses are particularly predisposed to tendon and ligament injuries accounting for approximately 50% of all musculoskeletal injuries to competing racehorses. However, some structures are much more exposed to injuries than others in this population of equine athletes.

Most tendon injuries in racehorses occur to the forelimb tendons, with overstrain injury of the SDFT at the very top of the list. This is particularly true in jump racing, where the prevalence of superficial digital flexor tendinopathy has been found to involve up to 24% of horses in training over 2 seasons (Avella et al. 2009) and could be considered as a “professional condition”. 

The higher exposure of tendon injury in jumping horses compared to flat racehorses might be explained by the fact they compete over longer distances, for more seasons and are generally older than horses that race on the flat. Another reason is very likely that the SDFT of jumping horses support bigger strains, and repetitively, when landing over fences. 

The main issue for this type of injuries is that tendon healing is slow and requires a long recovery between 10 to 18 months depending on the severity of cases. Although the scar tissue of tendon injuries can be optimised with an effective rehabilitation program, its functionality remains inferior with relatively high re-injury rates in the years following the original lesion. Thus, a complete understanding of SDF tendinopathy and its major risk factors in jump racing are very important to improve prevention and early management of the condition which is a potentially career-ending condition. In the racing community, it has become crucial given big issues it involves in sporting and economic terms, as well as for the health and the welfare of racehorses. 

SDF tendonitis - characteristics in jumping racehorses

SDF tendinopathy is one of the most common injuries in jump horses with a prevalence from 10 to 45% depending on epidemiological studies with some variations among trainers. Most of the cases involve the forelimbs, but hindlimb injuries also occur. Typically, lesions are found at the mid-cannon level in a central core lesion. 

The disruption of the tendon fibres might generally occur in this area because it appears to be preferentially loaded and degenerates more over the time. However, injuries of the SDFT can be seen at all the levels of the tendon. They are most commonly unilateral, but bilateral SDFT injuries can also occur.

Tendinopathy is a result of mechanical overload, varying from single fibril disruption to complete rupture of the whole tendon. The most common cause of SDFT overstrain injuries in NH horses is an accumulation of damages from repetitive overloading. 

The structure of the tendons in horses is matured around 2 years old, and after maturity there is very limited or no adaptation possible. It means that if tendons accumulate an excess of micro-damage over the time (tendon cells have a capacity to repair defects, but it is limited and need time), they become weaker with a loss of elasticity and strength leading to a point where higher SDFT loads / strains result in disruption of fibres with a clinical tendon injury. 

Moreover, it is important to be precise that forelimb flexor tendons in racehorses function close to their maximal load / strain-bearing capacity with a narrow safety margin. While failure of the SDFT has been shown occurring for tensile strain* from 12 to 20% in vitro, peak strains within SDFT at the gallop are by around 16%. Since racehorses operate close to the functional limit of the SDFT during fast work, any risk factors that lead to higher loads on tendons during training or racing can result in clinical injury with significant disruption of tendon fibres. Some of these in NH horses are discussed below.

* % increase in length from original length / tensile strain

Causes – Risk factors

Epidemiological studies have identified risk factors for SDF tendinopathy in racehorses. As discussed previously, jump horses are at greater risk than flat racehorses and it could be partially explained by horses being older in jump racing. 

Indeed, risk of SDFT injuries increases considerably with age and it appears that the prevalence in jump horses is more important in horses older than 5 years old, with the maximum injury rate seen in horses 12 to 14 years of age. 

Other major risk factors identified for SDF tendinopathy are frequent high-speed work, longer race distance, harder racetrack surface, heavier bodyweight and longer training career. Although they were not clearly identified as such, fatigue in relation with exercise duration or lack of fitness and conformation / shoeing (long toe, low heel) might increase the risk of SDF tendon injuries.  

In jump racing, SDF tendonitis appeared more common in steeplechasers than in hurdlers, but the reason may be the older age of the first ones rather than the type of racing. 

Diagnostic

Assessment of suspected tendon injuries should be based on history and clinical signs associated with diagnostic imaging. In many racing stables, people assess forelimb flexor tendons daily which can help to detect the early lesions of SDF tendinopathy. 

However, first signs may be very subtle and variable depending on history, severity and location of injury. They are usually noted within 24 hours of fast work or racing but can also develop at slower work. It is often subclinical and resolves quickly for non-severe injuries with acute lesions characterised by heat, soft tissue swelling and pain on palpation, whilst chronic ones appear with fibrosed thickening. 

Overstrain SDFT injuries are classically in the mid-cannon area and present a more or less severe change in profile of the back of the limb leading to the well-known qualification of “bowed tendon”.  

However, the obvious signs of inflammation (thickening and heat) are not always present even for some significant injuries and lameness doesn’t appear to be a very consistent feature associated with SDFT injuries. It is typically mild (1 to 2 grades out of 5 at the trot) and improves rapidly over the first week after the injury, however the tendon remains weakened. Consequently, the level of lameness and pain on palpation don’t have a good correlation with the severity of the lesion, except in the most severe cases.

In cases of apparent “bowed” injury with pain response on palpation, it is sufficient to consider there is likely an active tendonitis. In more subtle configuration, the need for ultrasound is indicated to confirm and assess the extent of the lesion.  

It may be best to perform or repeat tendon scans at 1 to 3 weeks after clinical injury first noted. Indeed, it allows us to assess lesion severity more accurately because of ultrasonographic underestimation of lesion extent at the beginning of tendon injuries. It is also very important in cases of suspected lesions but initially not well defined. 

Moreover, both tendons should be systematically examined on ultrasound for 2 major reasons. Firstly, SDFT tendinopathy are bilateral in up to 67% of cases (Webbon), and secondly it helps to differentiate active lesions versus subclinical changes on ultrasound (ex. “juvenile tendinitis”). A careful ultrasound assessment is also keen to exclude the presence of potential concomitant lesions (ex. SL desmitis).

When SDFT lesions are suspected, the horse should be put at stall rest with only short hand walking until the injury is confirmed or not by ultrasound a few weeks later.  

Ultrasound is routinely used by equine veterinarians and is elected to diagnose SDFT injuries as first-line diagnostic imaging. Whilst it is particularly relevant to document tendon lesions, it has been beneficial to develop a scoring system using specific measurements in order to categorise the severity of SDFT tendinopathy. 

It is also very useful to establish prognosis and monitor the healing process in line with an adapted rehabilitation program.

Prognosis and return for racing

The prognosis of SDF tendinopathy can be very variable depending on the severity of injury, the convalescence program and the type of racing. Overall, sport prognosis in the Thoroughbred is guarded with a reported return to racing from 20 to 60 % of cases. The major issue of tendon injuries in racehorses is the need for a long recovery and the high rate of re-injury due to poor regenerative capacity of tendon tissue, which is considered as a limiting factor for racing. However, return to training / racing activity is common for most mild / moderate SDFT injuries.

A study with jump racehorses affected by SDFT injuries classifying lesions severity by ultrasound established that all horses with mild lesions returned to training, and 63% raced. 50% of moderately affected horses returned to training, and 23% raced. 

In severe lesions, only 30% of horses resumed training, and 23% raced. In the study, the mean of reinjury rate for horses resuming work was 40% over a period of follow-up from 9 to 30 months, but some studies with longer follow-up reported up to 80% of horses sustaining a re-injury. Also, it is remarkable to note that a significant number of re-injuries affect the opposite normal limb.

Definitely, long-term prognosis is influenced by the severity of the lesions. The more severe SDFT lesions are, the lower chance of return to racing, shorter racing career and drop in racing class of those resuming there are. Complete ruptures of SDFT are hopeless for sport prognosis, but paddock life remains possible. 
The other factors established to influence the sport prognosis in racehorses affected by SDFT lesions are concomitant lesions, and more particularly bilateral tendinitis which have very poor prognosis. The less classical SDFT lesions like those at the level of carpal or proximal cannon have poorer prognosis for racing and ongoing lameness is frequently present. While it is difficult to study the influence of rehabilitation programs due to the need for a long period of follow-up, controlled exercise showed to provide better prognosis than only uncontrolled pasture rest. 

Treatment & Management: How to optimise the healing of tendon lesions?

Contrary to bone, healing of tendon lesions doesn’t allow you to get back pre-injury tissue due to its poor regenerative capacity. It means the structure and function of healed tendons are modified with different mechanical properties. Thus, the aim of SDF tendinopathies’ treatment is to optimise the healing process in order to get a strong and functional repaired tendon as much as possible. 

Although there are different options available in the management of SDFT lesions in racehorses, all of them should respect a long recovery with progressive return to work. As said previously, tendon healing is slow, and it is common to consider at least 12 months for return to racing in horses affected by SDFT injuries. 

To understand how to manage SDFT tendinopathy, it is important to consider the different phases in the tendon healing process.

In the initial days following the injury, the acute phase is characterised by inflammatory reaction. For a long time, it was advised to control quickly and aggressively the inflammatory response to limit damage to the tendon. However, it is now more and more controversial because the initial inflammatory phase would be beneficial for the repair process of tendons. 

The best management of this phase is to treat only in case of excessive pain and acute swelling through the use of anti-inflammatory drugs and cold therapy locally for a period of 3 to 5 days. During this phase, it is important to minimise exercise with stable confinement for the initial weeks. As we discussed previously, the ultrasound assessment of tendon injuries is generally best performed 1 to 3 weeks after the initiation of the injury because it allows to determine the full extent of the lesion. Thus, it is recommended to scan flexor tendons at the end of the acute phase to grade the severity of the lesion and establish a rehabilitation program and prognosis for return to racing activity. 

The other crucial period in the management of SDFT tendinopathy is the rehabilitation phase which can begin soon after the inflammation subsides. The cornerstones of healing tendon are the need for time and progressive graded and controlled exercise program. Protocols are quite empirical due to the difficulty to compare long-term outcome with homogenous groups. 

Indeed, the program should be determined in relation to the severity of the injury, but classically at least 6 months are necessary for return to cantering. A typical program is to introduce walking once the acute phase has passed with gradual increasing duration until 12 weeks. Ideally, monitoring of healing with ultrasound assessment every 3 months allows to control the evolution of the repair through an assessment of fiber pattern alignment and tendon/lesion size. In normal evolution, trotting can be introduced after 12 weeks and cantering after 32 weeks. Generally, the re-introduction to normal race training is resumed not before 8 to 12 months. Prognosis of SDFT lesions reported for horses rested for less than 6 months is poorer with higher risk of re-injury. 

Additional therapies can be used in the aim of optimising the healing of tendon tissue after injuries. Some of them are more and more popular and promising, but it is still difficult to evaluate and compare their efficacy. These modalities have to be considered as an additional intervention to graded exercise programs. 

The main interest of these therapies is not to reduce rehabilitation, but to optimise the healing process reducing the chance of re-injury after return to training. These additional therapies range from firing to intralesional therapies with PRP (Platele-rich plasma), PSGAGs (Polysulfated glycoaminoglycans), growth factors (IGF-1) or stem cells. To optimise the efficiency of these therapies, the treatment should be generally realised during the acute phase (more or less 2 weeks after the initiation of the injury). 

How SDF tendinopathy can be prevented in racehorses

Prevention is very important due to long recovery and guarded prognosis linked to high re-injury rate. 23–67% of horses with tendon injury treated using conservative methods will re-injure their tendons within 2 years of the original injury.

Strategies with success in preventing/reducing the incidence of tendon injury have not been validated; however, awareness of risk factors associated with SDFT tendinitis provides some useful guidance. 

• Avoid excessive training to fatigue and permit sufficient recovery time after racing or high-speed training. 

• Avoid use of poorly prepared or inappropriate track surfaces. 

• Long-term use of exercise boots/bandages may also contribute to increased risk; magnitude of this risk is unknown but should be balanced against rationale for routine use of bandages in horses that are not prone to interference injuries. 

• Strategies to reduce risk of reinjury of a rehabilitating/ rehabilitated tendon have also not been validated; however, it is rational to limit excessive loading of tendon. 

• Possible aspects to assist with above: incorporate treadmill use in training programme; attention to rider weight; minimise horse accruing excessive body condition; ensure maintenance of good dorsopalmar foot balance. 

• Possible benefit to be derived from regular post-exercise cryotherapy (such as cold water immersion): cooling the lower limb effectively can reduce enzymatic activity in tendon and potentially inhibit cell attrition resulting from high-intensity exercise. 

Tracks that are very hard result in higher speeds and increased peak impact loads. These fast tracks are therefore more likely to produce overstrain injuries of tendons. 

However, tracks where the surface is uneven, slippery, or shifty seem also to contribute to damaging loading patterns on tendons. Numerous factors influence the mechanical behaviour of a track surface; the weather and track maintenance have a major influence. Moisture content affects all tracks’ mechanical properties, and extreme temperatures appear to affect some synthetic tracks’ mechanical characteristics dramatically. 

Experience over years with a particular track type will allow identification of track conditions that may predispose to tendon injuries.

Fatigue is influenced primarily by the horse’s work schedule, level of fitness, and intensity of competition. Fatigue should be considered as a contributor to tendon injuries. With the onset of muscle fatigue, a horse’s stride characteristics change,13 altering the forces on the tendons. Fatigue in any sport results in an inevitable loss of form and coordination in each stride, which is likely to result in an increased risk of injury.

At high speed, lameness may result in excessive loading of the tendons in the contralateral limb.

Horses who are overweight or carrying excess weight will produce greater forces on their tendons compared with lower weight individuals.

Conclusion

In conclusion, tendon and ligament disorders prove to be a major cause of poor performance and lameness within the racing industry. With SDF tendinopathy being at the forefront of these lameness’, there are many strategies that can be adopted to prevent / reduce the incidences of tendon injuries within the thoroughbred.

To worm or not to worm? Addressing the dilemma of worming treatment decisions for horses in training

Article by Jacqui Mathews

All horses are exposed to parasitic worms at some point in their lives. It is not possible to eradicate all worms from all horses, nor completely avoid the risk of worm-associated disease, so some level of parasite control is necessary in any environment where horses are kept.   Traditionally, regular all-group wormer (anthelmintic) treatments were used to control these parasites, regardless of the management conditions. Increasing reports of wormer resistance over the last two decades [1] indicate this is no longer sustainable and will only act to worsen the situation, especially as no new wormers are coming to market any time soon. It is essential to take an approach that safeguards the effectiveness of anthelmintics. As common equine worms are spread via grass (Fig. 1), and horses in training do not routinely graze for significant periods (so are at lower risk of infection), they represent ideal candidates for diagnostic-led programmes.  

The worms that turned

The main worms of concern for horses in training are small redworms and tapeworms. Young horses (<2 years-old) may also be infected with ascarids. Small redworms can cause weight loss; in heavy infections (10,000s-1,000,000’s worms), this can be severe and accompanied by diarrhoea and/or colic. Tapeworms can cause colic but at a lower infection level; burdens of >20 tapeworms have been shown to cause gut damage. Ascarids are more likely to be problematical on studs; infections usually peak in 4-8 month-old foals, with a gradual reduction in susceptibility due to immunity. Immunity takes longer to develop against small redworms and tapeworms and a few horses remain susceptible throughout life, especially when exposed to heavily-contaminated paddocks and/or have medical conditions that affect their immunity. 

Wormers available include fenbendazole, pyrantel salts (double dose for tapeworms), ivermectin, moxidectin and praziquantel (tapeworms only). Resistance to these wormers has been reported in small redworms (benzimidazole resistance is ubiquitous, with reports of resistance to all other wormers), ascarids (especially resistance to ivermectin) and tapeworms (pyrantel and praziquantel resistance was recently reported [2]). If effective worm killing is not achieved due to the presence of resistance, a situation could occur where veterinarians are unable to effectively treat horses that present with disease due to heavy burdens. It is therefore essential to reduce the amount of wormers administered and only treat horses when an assessment indicates that worming is necessary.

Risk assess to consider if horses are likely to be infected with worms

Be aware of the risk factors for worm infection, with age and access to contaminated grass key features. As most horses in training have no/limited access to pasture, they should be at low risk of infection, especially horses >4 years. Yearlings, 2- and 3-year-olds are more likely to have higher burdens, especially small redworm; this should be taken into account when planning testing and treatment options (see below). Older horses (>15 years), used as riding horses or companions, may also have higher burdens so can act as potential sources of contamination. 

Regular assessment with your veterinarian of the risk of infection to the individual or group enables danger zones in management practices to be identified, addressed, and the impact of improvements monitored over time. Include sufficient detail in the assessment so that seemingly innocuous practices that increase risk (for example, short daily turn-outs) can be identified and action taken. Risk assessment will:

1. Inform which tests to perform, test frequency and which horses to include 

2. Indicate the need for strategic treatments; for instance, small redworm larvicidal therapy in high-risk (younger) horses where tests cannot be used to guide treatment decisions

3. Provide information on potential worm exposure and the need to reduce the opportunity of horses being infected (at the yard or elsewhere).  

Tests provide information to help treatment decisions

Diagnostics are essential for making informed decisions about worming and for selecting which product to use, whilst reducing selection for resistance. Tests available include faecal egg count (FEC) and antibody-based assays. 

FEC tests estimate the number of worm eggs a horse is passing in dung (a measure of contamination potential) and provide information on the type of eggs excreted. On racing yards, testing is recommended every 12-16 weeks.  Usually, ~80% of horses excrete ~20% of the eggs passed [3], meaning that many individuals have no/low worm egg shedding and will not need treatment, thus preserving wormers. Horses estimated as passing >200 to >500 worm eggs per gram (epg) dung are recommended for treatment. When collecting a dung sample, select at least three balls from the pile, with a minimum of 5 grams placed in a pot/bag with all air excluded and the samples kept cool. FEC reduction tests should be conducted once a year to provide information on effectiveness of the wormers being used to target small redworm. 

FEC tests only detect the products of egg-laying adult worms and are not reliable indicators of the burden within an individual, especially as male and immature worms are not detected. In the case of tapeworm, FEC methods are also affected by inconsistent release of egg-containing segments from adult worms so are not recommended for identifying infection with this parasite. Instead, tests that detect antibodies can be utilised to provide information on the level of tapeworm or small redworm infection in individuals.

Tapeworm antibody tests are available in saliva and blood formats. Both work on the principle of measuring worm-specific antibodies, levels of which show a strong positive relationship with tapeworm burden. The tests have been shown to accurately identify all horses that harbour clinically-relevant burdens of >20 tapeworms [4]. Testing identifies horses that will contaminate areas where horses graze, as well as those harbouring burdens that may put them at risk of colic. All horses should be tested at the same time to identify those that need anti-tapeworm treatment; ideally, in combination with tests that detect small redworm infection (FECs or small redworm blood test). By doing this, the correct worming product can be selected based on the test data (Fig. 2). Testing can be performed once or twice a year, depending on the level of risk identified at the initial assessment and informed by ongoing data. Tapeworm testing results in large reductions in anthelmintic use; from 2015-2022, >164,000 UK horses were assessed using the saliva test and only 1/3 were recommended for treatment [5]. In the unlikely event where many horses test tapeworm-positive on a yard, the source of infection needs to be identified and management rectified to reduce transmission via oribatid mites.

It was previously recommended to treat all horses for small redworm encysted larvae in late autumn/winter. As it acts to select resistance, routine all-group treatment is no longer advised for horses at low risk of infection. Horses in training will usually fall into this category. For low-risk horses, the options are to not administer this treatment, or use the Small Redworm Blood Test. Similar to the tapeworm tests, this measures worm-specific antibodies and demonstrates high sensitivity in identifying horses with low small redworm burdens that do not require treatment. The test can be utilised in autumn/winter when it is more likely that small redworm encysted larvae, that are not detected by FEC tests, are present. Applying the test in low-risk sport horse groups demonstrated that many horses (>60%) fell below the low 1,000-small redworm threshold [5]. 

Horses in training can test positive by any of these methods, despite the fact that they do not graze for significant periods. This is because they can become exposed to worm infections during short turnout periods, or if they are allowed to graze on training grounds or at the race course. Wherever there is dung deposited, there may be worms!   

In the case study (Fig. 3), tapeworm and small redworm serum scores in December are shown from horses based at a training yard in the UK. The results demonstrated negligible burdens (<1,000 worms) of small redworms in ~1/3 of the group, with only 14% of horses recommended for tapeworm treatment. These horses had 30 minutes turnout to a small paddock each day; dung was not removed from this paddock, providing a source of worm infection. The veterinarian subsequently advised the trainer to remove dung daily from the paddock and to treat test-positive horses with a larvicidal anthelmintic and, where indicated, an anti-tapeworm treatment. These horses previously received regular all-group treatments, so although blood testing recommended a proportion to be wormed, this strategy reduced worming frequency overall and, importantly, provided the trainer with insights regarding management procedures. 

Advice for horses new to a yard

The introduction of newcomers or the return of previous residents to a yard risks introduction of ‘new’ parasites. All new arrivals should be isolated, tested (FEC/small redworm blood test, tapeworm test) and wormed based on the results. For small redworm, a FEC reduction test should be performed to assess wormer sensitivity of the parasites the horse is carrying. Ideally, keep the horse away from grazing in the interim, or at least prevent access to turnout paddocks for 3 days after worming to stop transmission of eggs that are excreted after treatment. 

In conclusion 

Few studies have examined worm prevalence, control practices or effectiveness of anthelmintics on training yards. Those that have, indicate industry-wide overuse of wormers, with few trainers using evidence-based methods [6]. The racing industry must avoid the legacy of spreading drug-resistant worms to other parts of the sector.  Once horses retire from training, they enter a spectrum of environments where the introduction of wormer-resistant parasites could prove extremely detrimental, particularly, breeding enterprises where susceptible young animals will co-graze with mares, or retirement homes/sanctuaries containing geriatric horses that may be more prone to worm-associated disease. The introduction of drug-resistant parasites to leisure riding establishments or yards focused on eventing, show jumping or dressage, would be viewed as a negative sequelae of the over-use of anthelmintics in the training sector. Given the amount of attention paid to the health and physiology of racehorses, trainers, working with their veterinarian, are perfectly poised to adopt worm control plans designed to meet the needs of the individual by following a diagnostic-led approach. An exemplar control plan is shown in Fig. 4.

References

1. Nielsen 2022. Int J Parasitol Drugs Drug Resist. 20;76-88.

2. Nielsen 2023. Int J Parasitol Drugs Drug Resist. 22:96-101.

3. Relf et al. 2013. Parasitology 140:641-652. 

4. Lightbody et al. 2016. Vet Clin Pathol. 45:335-346.

5. Matthews et al. 2024. In Practice 46:34-41.

6. Rosanowski et al. 2016. Equine Vet J. 48:387-93.

Suppressing unwanted hormonal behaviours in training

Article by Kate Dugher

The desire to suppress unwanted behaviour in the horse can present for many different reasons. The behaviours that we are talking about can be anything from poor performance to hyper-excitability, distraction, discomfort on girthing up, not responding to the jockey, bucking, rearing, squealing, kicking or aggression.  

Often it is assumed that overt behaviours are hormonally driven; however, it can be easy to discount many other possible causes of these behaviours, especially those that are related to pain.  A full clinical examination by a veterinarian is always warranted when considering unwanted behaviour in the horse in order to appropriately identify the cause and consider the most appropriate treatment options. 

Common causes of abnormal/unwanted behaviour can include: 

• Musculoskeletal pain (lameness)

• Gastric ulceration

• Dental disease

• Poorly fitting tack

• Stress

• Hormonal influence

• Learnt behaviour 

There are also many reasons for normal and abnormal behaviours that can be associated with the reproductive system. Some of these could be identified as undesirable behaviours when associated with performance. 

The equine reproductive cycle

Horses are seasonal long day breeders and are influenced by daylight length. This means that the majority of mares have inactive ovaries in the winter and do not exhibit oestrus behaviour during this time. In comparison, in the summer months, they exhibit a reproductive cycle that lasts an average of 21 days. They spend, on average, 5-7 days in oestrus, ‘in season’, and 14 days in diestrus, ‘not in season’. 

In the spring and autumn months the mare undergoes a transitional period. During this time, oestrogen concentrations are variable, and oestrus behaviour can be seen irregularly. Whilst stallions are also affected by seasonality, they still exhibit reproductive behaviour all year round. The mare’s reproductive cycle can also be influenced by artificial light and therefore, it is worth considering that performance horses who are exposed to stable lights beyond the normal daylight hours in spring, autumn or winter may cycle for a longer period of the year or even throughout winter. 

Puberty

Timing of puberty in the horse is varied and affected by both genetic and environmental factors. Not only by age but also by time of year in which they were born, body condition and social cues. Puberty in fillies is usually at around 12-19 months compared to colts at around 10-24 months, however, there are wide variations from these reference ranges. 

Normal reproductive behaviour in the mare

Normal oestrus behaviour occurs under high oestrogen and low progesterone influence. Commonly associated behaviours include receptivity to stallions/geldings, vocalisation, increased frequency of urination and presentation of hindquarters in a wide based stance.

Normal diestrus behaviour under a dominant progesterone state includes repulsion to the stallion and can occasionally be associated with aggressive behaviour to other horses. During pregnancy, the mare will also be under a dominant progesterone influence and is unlikely to exhibit oestrus behaviour particularly in the first trimester. Later in gestation a peak in testosterone and oestrogen levels may be associated with changes in behaviour. 

Abnormal reproductive behaviour in the mare

Ovarian pain

Many mares will show an obvious reaction upon rectal palpation of the ovary when close to ovulation, suggesting that the dominant follicle/ovary can sometimes be tender at this time. Comparatively, humans often describe some ovarian pain around the time of ovulation. Therefore, it can be assumed that some mares could also experience discomfort around the time of ovulation. 

Other possible causes of ovarian pain that can occasionally occur in normal cyclicity include ovarian haematomas and haemorrhagic anovulatory follicles. It is also a consideration that external pressure placed onto the lumbar region close to the ovary around the time of ovulation could rarely elicit a painful response in some individuals.  

Vaginal pain

Vaginal pain has occasionally been associated with conditions such as vaginitis and pneumovagina. These conditions describe inflammation and/or air in the vagina. These are most commonly associated with poor perineal conformation and can be evident in some performance mares. 

If vaginal pain is suspected due to poor perineal conformation, then placement of a caslicks vulvoplasty may prove to be beneficial. If concurrent infection or urine pooling is suspected, then further intervention may be required. 

Reproductive tumours 

Reproductive cancer affecting the ovaries is one of the most common causes of cancer in the mare, the most common being the granulosa theca cell tumour (GTCT). These are generally locally invasive and are unlikely to cause any further health problems if the affected ovary is removed. They are often identified with a change in behaviour. On rectal examination a common finding would be to identify one enlarged and one small ovary. 

Depending on which reproductive hormones the tumour secretes is likely to influence the associated behaviour. This can include stallion-like behaviour, aggression, persistent oestrus behaviour or complete absence of reproductive behaviour. The severity of this often depends on the stage at which this condition is identified. Other types of ovarian tumours are less common but depending on if/which hormones are secreted will dictate which hormonal behaviours are associated. It is suspected that occasionally there could be ovarian pain associated with some of these cases particularly when the ovary is very large in size. 

Reproduction related treatment options

Mares

To have the most successful outcome in controlling reproductive hormonal behaviour in the mare, it is important to understand whether the unwanted behaviour is being exhibited all year round or just in the summer months and whether it is related to a particular stage of the oestrus cycle. 

Whilst it is commonly assumed that most behaviour problems are associated with the mare being in season, occasionally some mares can show unwanted aggressive behaviour under the influence of progesterone – when they are not in season. 

Furthermore, it can be tricky to interpret this when trying to link hormonal behaviours to performance based unwanted behaviours and these signs can often be very individual. Keeping records of behaviour versus stage of the reproductive cycle can help to try and decipher whether reproductive hormones are likely to be playing a part in the unwanted behaviour. However, this does require careful monitoring and, most likely, multiple reproductive ultrasound examinations. 

The other consideration is that unwanted behaviours are related to reproductive pain or abnormal hormone production due to pathological conditions of the reproductive tract as previously described. 

Ways to mimic the diestrus state and suppress oestrogen related behaviour

Progesterone/Progestins 

Progesterone is the dominant hormone produced by mares in diestrus. There are a multitude of systemic progestin (progesterone-like medications) available for use in horses in injectable and oral formulations. 

Altrenogest is a synthetic progestin commonly used to suppress oestrus behaviour by acting as a progesterone agonist. This means that the horse is likely to exhibit normal diestrus behaviour for that individual whilst it is being administered. Altrenogest is molecularly very similar to the anabolic steroids trendione and trenbolone. Occasionally the product may contain trace levels of these anabolic steroids. Therefore, its use for horses in training is to be taken with extreme caution and withdrawal times adhered to. It is banned for use in racing thoroughbreds in some countries. 

There is also evidence to show that altrenogest can exhibit a reduced stress response and sedative-like effects in some horses, particularly mares. This effect may be beneficial in anxious individuals in training circumstances. However, arguably, dependent on the individual, a reduced stress response could have either a positive or negative effect on performance. 

Injectable progesterone applications have been used in racing thoroughbreds with appropriate clearance times before racing. These are often available in oil-based preparations which are commonly associated with injection site reactions and therefore, many trainers would avoid administering these within 3 days of racing. 

Upon cessation of progesterone supplementation, many mares will present with oestrus signs 2-7 days after treatment, as this mimics normal luteolysis at the end of the diestrus phase. Therefore, the timing of administration and cessation of progesterone/progestin treatments is a crucial consideration when being used for the prevention of oestrus behaviour.

Intra-uterine devices (IUDs)

IUDs have been historically utilised to mimic early pregnancy in the mare with varying success. These require an ovulation to act upon to extend the life of the corpus luteum by blocking the hormonal release that normally brings them back into season. Therefore, they are only useful once the mare is already cycling. 

Glass marbles have been the most used IUD historically; however, these are no longer recommended due to multiple evidenced side effects including risk of glass fragmentation in the uterus. The use of PMMA spheres or magnetic devices such as the iUPOD would be a preferable and safer alternative if an IUD was going to be used.

Interestingly, in the author’s experience speaking with clinicians who have administered these devices, there is surprisingly positive client satisfaction despite the inconsistent and variable evidence of the success of these devices in the literature. 

Oxytocin

Administration of the hormone, oxytocin, at specific time points when the mare is in diestrus can extend diestrus by up to 60-90 days. This technique is evidenced by multiple studies. For optimal success, reproductive ultrasound would be used to identify ovulation and carefully plan the timing of injectable administration. 

However, some studies have also evidenced successful extension of the diestrus phase without known timing of ovulation. The major downside of this technique is the need for administration of multiple injections/multiple reproductive examinations to time ovulation. 

Immunological approach

Gonadotrophin releasing hormone (GnRH) is a hormone produced by the brain that is responsible for stimulating follicle growth in the ovaries and activation of a hormonal cascade to bring the mare into oestrus. 

GnRH vaccinations generate an immune response against GnRH, suppressing the hormonal cascade and ovarian activity and therefore, oestrus behaviour. An equine licensed product has previously been available in Australia. However, this is no longer in production. We have the option of a swine formulation, Improvac®, which has commonly been used in equids off licence. 

Major drawbacks for the use of this are common adverse injection site reactions, risk of anaphylaxis and concern over extended length of ovarian suppression. Therefore, this option would not be recommended in mares with a future breeding potential. 

Surgical approach

Ovariectomy is a treatment option for hormonal behaviour in mares. The ovary is the only supply of progesterone in the horse but is not the only supply of oestrogen. 

Ovariectomy has been associated with good client satisfaction in many cases to resolve unwanted hormonal behaviour. However, in some mares, whilst removal of the ovaries would prevent cyclicity, it can occasionally result in persistent oestrus behaviour in the absence of progesterone produced by the ovaries. This is also a permanent option that will remove breeding potential.

The techniques discussed so far are not exhaustive and there are many other methods that have been used to affect cyclicity or hormonal behaviour including pregnancy, induction of diestrus ovulation, GnRH analogue medication and infusion of intrauterine medical grade plant oils. 

Colts/stallions

There are a few medicated options for hormonal manipulation in males. Progestagen administration e.g. oral altrenogest administration can quieten stallion like behaviour in males but is banned for use in racing and training. 

Immunisation with off licence GnRH vaccines such as Improvac®, suppresses pituitary-gonadal hormone production aiming to cause a ‘chemical castration.’ However, results can be variable, particularly in mature stallions. As mentioned previously with mares, the downside of these vaccines are injection site reactions, risk of anaphylaxis and risk of prolonged sterility in future breeding animals.

Occasionally nutritional supplements have been used with effect in stallions such as L-tryptophan, a precursor of the neurotransmitter serotonin. This has induced calm and fatigue-like behaviour in a number of species. 

Synthetic preparations of calming pheromones based on an equine appeasing pheromone produced in perimammary gland secretions of lactating females have also been used with such success. Of course, the use of these to calm behaviour vs the desire to generate an athletic performance animal is a consideration and results are likely to have wide individual variation.

Understanding and treating depression in horses

Introduction

While depression is widely recognised in humans, it is a condition which is often overlooked in animals. The symptoms and clinical signs of depression vary from species to species but recent studies have shown that humans and horses share some characteristic warning signs which are important to recognise.  

Horses are prey animals with a well-developed fight-or-flight response and their behaviours are controlled by the nervous and endocrine system.  Like all animals, behaviour is influenced by many external factors that include genetic predisposition, environment, physiology, experience and learning. Foals are neurologically mature at birth and soon after birth can identify and react to dangerous stimuli, but like humans, the horse’s brain function does decrease with age resulting in increase in anxieties and fears. 

The brain and its neurotransmitters play an instrumental role in the temperament and behaviour of the horse; therefore, abnormal levels of various hormones can lead to a change. Normal survival instincts for the horse fall into two broad categories that includes ‘something to fear and must flee’ and ‘something not to fear and should be explored or ignored’. New research has also demonstrated that there is not a linear dominance hierarchy but rather the herd communicates with positive reinforcement and less from punishment.

In order to achieve the best results when training, it is important to consider these natural behavioural instincts. Maintaining a positive mental attitude in both training and management regimes for the horse will have considerable benefits to performance and reduce negative behaviours. 

What is depression? 

Depressive disorder (also known as depression) is a mental disorder that can occur in horses.  It involves a depressed mood or loss of pleasure or interest in activities for long periods of time.  Depression affects how the horse thinks and behaves and may lead to a variety of potential physical problems.  

While depression is widely recognised in humans, it is an illness which is often overlooked in animals.  The symptoms and clinical signs of depression vary from species to species but recent studies show that humans and horses share some characteristics. With racehorse welfare being a key topic at present, understanding and recognising small behaviour changes can allow for small management adaptations to be made thus enhancing the horses wellbeing. 

The research 

Recent research from France alongside the growing body of research, suggests that horses may develop something similar to depression in a response to physical or social discomfort.   

Researchers have observed horses that become withdrawn because of undergoing a cognitive shift.  It has been found that horses tune out to their surroundings due to physical or psychological stress.  Horses have the cognitive ability to be attentive; however, with the presence of chronic stressors there is a delay in a horse's response as they have “switched off” from their environment and demonstrated sensory inattention. 

Because we do not truly know how the horse is feeling, the hypothesis currently being considered is that the horse develops an “inward-oriented attention” when subjected to chronic disorders.  It must be stressed that this long delay in attentiveness does not indicate a state of calm for the horse but a withdrawal from its surroundings. 

Dr Georgia Mason from The Ontario Veterinary College has suggested that a horse may respond similarly to humans with depression.  It is thought that the horse’s withdrawal can be a result of a ‘learned helplessness’ in that responding to negative stimuli does not make any difference.  Thus depressed people are prone, for example, to judge ambiguous stimuli as being unlikely to be positive and to recall unpleasant memories more readily than pleasant ones.

In addition, a number of studies have assessed cortisol levels in those horses that are withdrawn. Cortisol acts to assist in relieving stress by increasing glucose metabolism to provide energy, which then enables the horse to escape from the stress. In the short-term, cortisol release is beneficial to the horse to help it cope with a stressor. This study found that abnormally low levels of cortisol (hence a physiological depression) were found in withdrawn horses that are in a pathological and depressed state.  These depressed horses also expressed anhedonia, which is the loss of pleasure to feed on an appetent substance.  

Further studies and research are needed to better understand the pathology of depression in horses.  It has been suggested that the life conditions, such as food, space, social conditions and health problems should be questioned and observed in order to identify potential acute or chronic stressors that may lead to depression. 

However, there are reviews that question the current animal models of depression and suggest that ethological models of mood disorders based on animals living under natural conditions need to be improved and developed. 

Symptoms of a depressed horse 

It is important to become acquainted with potential signs of depression in the horse so that you can identify them quickly.  By identifying the symptoms of depression, one can rapidly begin the task of identifying the underlying cause such as an injury, illness, social or environmental stressor.  With these tools, one can reduce the risk of the short-term and long-term negative effects that could ultimately hinder the horse’s health and performance.  

Lack of response

In humans and animals, being attentive is one aspect of subject cognitive abilities and capacities. The delay in responding to stimulation shows that withdrawn horses ‘switch off’ from their environment and show sensory inattention. Such lapses of attention are likely to be associated with the chronic effect of stressors, which might be expected to induce a lowered state of arousal.

A French study from the Universite de Rennes, demonstrated that depressed horses that were subjected to a series of five new, unique and unusual sounds were significantly less likely to pay attention to the noises compared to normal horses.  Their findings demonstrated that the withdrawn horses had undergone a cognitive shift that they were so physically or psychologically stressed that they developed sensory inattention. 

Heightened anxiety 

While the depressed horse will often be disinterested in everyday activities, people and companions, they are likely to demonstrate heightened emotions towards challenging situations and new stimuli as they try to express their discomfort. Stimuli that are usually unremarkable to the horse may become uncomfortable for the horse and make them “spooky”, anxious or fearful when they weren’t before. 

Lack of interest in food 

A change in mental well-being in your horse can lead to a loss of appetite.  The potential complications are the loss of weight, condition, muscle development, fitness, energy levels as well as the increased susceptibility to infection and prone to other health conditions such as colic or gastric ulcers. 

There are other illnesses and ailments that can lead to inappetence; hence, it is worth seeking veterinary advice in order to rule out any other physical problems.  

Anhedonia

Dr Carole Fureix looked at anhedonia which is the loss of feeling pleasure from experiences that used to be pleasurable.  This symptom is prominent in the depression of humans. Her study demonstrated that horses who are at times withdrawn are more anhedonic than those that are not withdrawn.  She concluded that this is a key symptom of clinical depression and suggests that withdrawn horses are indeed in a depression-like state.  

The horse may show unwillingness to work or no longer take pleasure in work they used to enjoy. This is especially important when considering rider and horse safety too as a withdrawn horse may not react appropriately to potentially dangerous situations.

Posture

Standing facing the stall wall for periods of time while demonstrating a withdrawn posture showing a fixed gaze, neck stretched out level with back, eyes open but lack of eye and ear movement. This differs from a content horse that is resting and displaying relaxed muscles, laterally rotated ears, the drooping of its eyelids and lips and holding its neck such that it slopes lower and rounder.  

Physical changes are perhaps somewhat easier to spot with a withdrawn posture being one of the typical signs of depression.  A healthy and content horse will stand with their head up and ears moving inquisitively.

Causes of depression 

The domesticated horse is often managed in such a way that they cannot express their natural behavioural instincts, thus exposing them to stressors which can lead to depression.

Lack of adequate positive social interaction with other horses 

A study from Michael Steger and Todd Kashdan explained that dysfunctional social behaviour has been implicated in the experience of depression. 

In addition, Timothy Elmer and Christoph Stadtfeld described individuals with depressive symptoms are more likely to be isolated from their social group(s), which can further increase their symptoms.  

Similarly, lack of social interaction without conscious choice for extended periods of time can lead to depression in humans.

Lack of adequate exercise and/or turnout 

It is well documented in human medicine that exercise and physical activity can improve many health conditions. Research on depression, anxiety and exercise demonstrates that the mental health and physical benefits can help improve mood and lessen anxiety.  The link between depression, anxiety and exercise are not entirely clear.  It has also been shown that exercise and physical activity may help keep depression and anxiety from coming back. 

Companionship reduces stress in the horse, hence naturally  living in a herd.  Horses are able to form companionships with their own species and other animals including humans.  In fact, horses kept in isolation, such as in closed stables, can become anxious, flighty and difficult to manage. 

Exercise releases endorphins which are feel-good chemicals in the body and also allows for more social interaction.  A recent University of London study demonstrated that people with low aerobic and muscular fitness are nearly twice as likely to experience depression.  

Illness or injury that causes pain or discomfort 

In humans studies have found that anywhere between 30-85% of patients suffering from chronic pain are also clinically depressed. Other illnesses in humans such as nutritional deficiencies, cushing’s disease, lyme disease, chronic pain, and insulin resistance can cause depression.

Stress during training, competing or in the daily routine 

If there is chronic stress in which the horse’s physiological stress response is taxed beyond what it is designed to do it can begin to impair the horse possibly leading to depression 

Inflammation and depression 

There is evidence that there is a link between inflammation and depression. Inflammations that lead to serious depression in humans can be caused by infections such as those caused by bacteria, viruses or even parasites.  There is increasing evidence that inflammation can cause depression because of the increase of cytokines setting the horse’s brain into “sick mode”.   

Treating depression

Simple changes in management can help treat the underlying cause of depression and can substantially improve the horses well-being thus having a positive impact on performance.

Light therapy

Modern management methods mean that horses can spend a large amount of time stabled which impacts the horse’s circadian rhythm (body clock). 

A study was performed at Nottingham Trent University where trial horses were put under an hour of high intensity broad spectrum light every day for six weeks. Their behaviours regarding feeding, sleep patterns and attitude to being handled and ridden were compared to a group of horses that had not received the therapy. The untreated horses were noted to be sleeping longer, lazier at ridden exercise and grumpier.

Light therapies have many positive benefits that can reduce signs of depression and improve overall well being; better daytime alertness and improved rest and sleep pattern, extending summer coat and body condition and encouraging the body to convert feed to muscle mass, noticeably fewer stable vices such as box walking, cribbing, weaving and reduced bacterial pathogens and fungal load leading to improved respiratory function.

Management

Racing is already making moves to ensure the best welfare conditions for horses, with German trainers now having to comply with regulations regarding size of stable, the amount of light in the stable, the provision of windows enabling horses to socialise and turn out capacity for a minimum two hours per day.

Increasing turnout time is reported to have positive effects on their horses' mental wellbeing, reduces stiffness and lowers the rate of stable vices. It also allows the horse to make social connections whilst allowing them to show their natural instinctual behaviours. 

With horses in varying routines in large yards, this can sometimes become stressful to some individuals. By providing company of other horses when stabled, this can help with social interactions and reduce stress. Stable enrichment and adlib forage can also replicate positive behaviours in the stable. 

It is known that exercise releases ‘feel good’ endorphins, thus, keeping the horse in a regular training regime complimented with the correct nutrition will be beneficial. 

Veterinary advice

It is important to seek veterinary advice should the horse be exhibiting signs of depression to help identify the underlying cause. Diagnostics such as blood tests can ensure there is no infection present and work-ups will highlight any pain or discomfort.

Conclusion 

While depression is widely recognised in humans, it is an illness which is often overlooked in animals. Depression in horses can be significant and harmful regardless of the underlying cause and can be temporary or long term. It is vital to ascertain the underlying cause of depression in a horse in order to treat and remedy the illness. 

Reducing Wind Surgeries in Thoroughbreds: Harnessing Field Data for Genetic Selection

Article by Dr Erwin Koenen and Richard Birnie

Wind Surgery (WS), also known as ‘wind operations’ or ‘wind ops’, is a term used to describe a collection of surgeries performed on the upper respiratory tract (URT) of the horse, typically the larynx (throat). These surgeries aim to alleviate conditions that cause obstruction of airflow and, therefore, limit oxygen supply to exercising muscles, impacting athletic performance. 

Although WS is generally an effective treatment of upper airway conditions, there is growing interest in curbing them for both animal welfare and financial reasons. For many years, trainers and breeders have considered endoscopic data when buying at sales. Selecting horses with better scoping data for racing and breeding is expected to reduce the risk of URT-related diseases and resulting surgeries. Breeders might realise additional reductions if they could also consider information on the variation in WS among progeny groups when making selection decisions. 
In 2018, the British Horse Racing Authority (BHA) introduced the requirement that trainers declare if a horse racing in Britain has had a WS since their previous race. This routinely collected field data may support the promising avenue of reducing WS by genetic selection. 

In this article, we discuss the different types of surgeries, the use of endoscopic examinations and the opportunities and challenges of leveraging WS declarations for genetic selection.

Wind Surgeries

The term ‘wind surgery’ encompasses the following surgical procedures:

• Tie-back, also known as a prosthetic laryngoplasty. This is utilised for the treatment of roarers, also known as recurrent laryngeal neuropathy (RLN). 

• Hobday procedure, also known as a ventriculectomy or ventriculocordectomy. This is also utilised in the treatment of roarers and is frequently performed in conjunction with a tie-back procedure. 

• Tie-forward, for the treatment of dorsal displacement of the soft palate (DDSP)

• Soft palate cautery, for the treatment of DDSP.

• Epiglottic entrapment surgery, for the treatment of epiglottic entrapment (EE).

Wind surgeries can have welfare implications, for example, if a horse suffers post-surgical complications such as infection or difficulty swallowing. Wind surgeries can also have significant financial implications due to the cost of the surgery itself and the potential loss of earnings due to time off for the procedure. Many WS procedures have widely reported high success rates; for example, it is realistic to expect horses undergoing a tie-back procedure to have success rates of 70-80%, a figure considered to be irrespective of the degree of RLN present. However, no surgical procedure is 100% effective in treating their respective upper airway condition. This means that a certain percentage of horses requiring WS will not return to the same pre-athletic ability they had prior to disease development, again having financial implications on a horse’s potential winnings.

Information on the proportion of racehorses that have had a WS is scarce. To get a preliminary estimate, we studied the WS declarations of 1,000 randomly selected racehorses that ran in Britain between January and May 2024. In this sample approximately 15% of the horses have had at least one WS in their career. As expected, higher frequencies were found for horses in National Hunt races than in Flat races.

Endoscopic Examinations
Early detection of conditions requiring WS is difficult as they do not typically manifest in youngstock but instead frequently present during a horse’s athletic career. Thoroughbred racehorses typically present for surgical management of RLN at 2-3 years of age. Despite this, at most major thoroughbred yearling sales, individual animals undergo post-sale URT endoscopic examinations to assess for disease processes affecting the upper airways, including RLN, DDSP and EE amongst several other conditions. The presence of any one of these disease processes allows for the prospective purchaser to cancel the sale.

Several studies have found a relationship between endoscopic observations in yearlings, particularly the incidence and severity of laryngeal pathologies such as RLN, and later racing performance. The most recent study examined 1,244 Australian thoroughbred yearlings’ URT endoscopic examinations and suggests that resting laryngeal function, associated with the degree of RLN, can be a useful predictor of future racing performance and earning potential. For example, the mean earnings of yearlings graded with a ‘normal’ larynx (condensed Lane scale) was AU$20,100 (£10,453 / €12,271) whereas it was only AU$1,000 (£520 / €610) for those graded with an ‘abnormal’ larynx. 

Although the URT endoscopic data set collected from yearling sales has many valuable applications, these are typically more pertinent to purchasing recommendations and is unlikely to be used for large-scale genetic evaluations. 

Genetic evaluation of WS 

The feasibility of genetic evaluation based on routinely reported WS data largely depends on the presence of natural genetic variation, which may differ per individual surgeries. Heritability estimates, indicating the relative contribution of genetics, for the individual surgeries are not yet known. However, moderate to high heritabilities have been reported for RLN, one of the conditions often requiring WS. Several studies have reported a positive genetic correlation between height and RLN, with taller horses having an increased risk of RLN development. It has been hypothesised that selecting against these genes could result in a shorter population of horses which may impact on athletic performance. Although the exact mode of inheritance remains largely unknown, it is speculated to be polygenic, with numerous genes contributing incrementally to the overall genetic variation and development of RLN. We generally also assume that genes from both parents on average contribute equally to the risk of RLN. Research into the genetic components of DDSP and EE is very scarce.

Once the genetic variation of WS data has been confirmed, breeding organisations can develop statistics indicating the genetic quality of individual horses. A first possible step in this direction might be publishing the average WS incidence for commonly used sires. A more advanced step might be a genetic evaluation based on WS data and pedigree. Such statistical procedures, already routinely implemented in many livestock breeding programmes, optimally combine family information and adjust for non-genetic effects such as age and sex. Breeders can use the resulting estimated breeding values to better identify stallions and mares with a lower genetic risk for requiring WS. The reliability of an individual breeding value depends on the amount of data used, which is low for horses with no offspring and limited pedigree information but high for sires with many offspring. 

Another potential data source for breeders is DNA testing based on the relationship between mutations in the DNA and the inherited predisposition for WS. Although genome-wide association studies (GWAS) have identified variants that relate to RLN, their predictive value has been too low to develop and commercialise highly reliable DNA tests. However, the use of estimated breeding values based on field data may boost the power of ongoing GWAS studies to identify predictive variants.

Impact of genetic selection

Genetic selection operates as a long-term strategy, with noticeable improvements materialising in subsequent generations, albeit typically in modest increments. Nonetheless, experiences with breeding programmes in other livestock species, such as cattle, pigs and poultry, underscore the transformative potential of systematic selection in reshaping population dynamics over time. Unlike non-genetic interventions such as nutrition or training, the outcomes of genetic selection are permanent and cumulative. Moreover, genetic selection often proves cost-effective, especially when leveraging existing data collection practices. 

However, for the widespread adoption of genetic selection against WS within the industry, stakeholders' acceptance is crucial. While publishing breeding values fosters transparency and aids genetic progress, it may encounter resistance from some owners unaccustomed to such openness. Furthermore, given that many Thoroughbred breeders lack familiarity with rational selection based on breeding values, there is a risk of misguided expectations and insufficient support within the sector. Hence, collaborative efforts with stakeholders are imperative both in the development and utilisation of genetic metrics for health and welfare traits to ensure their integration into breeding practices.

Conclusion

The wealth of recorded WS field data in Britain, which was initially intended for the betting public, offers an exciting prospect for exploring its potential application in genetic evaluations. This dataset provides an unprecedented opportunity to reliably study the genetic variation of commonly occurring URT conditions requiring WS. Continued research into the components of the underlying operations, coupled with robust stakeholder engagement, holds promise for yielding valuable insights. Ultimately, such endeavours could empower breeders to implement strategies aimed at effectively mitigating the prevalence of WS within the Thoroughbred population.

References

• Ahern, B.J., A. Sole, K. De Klerk, L.R. Hogg, S.A. Vallance, F.R. Bertin and S.H. Franklin, 2022. Evaluation of postsale endoscopy as a predictor of future racing performance in an Australian thoroughbred yearling population. Aust. Vet. J. 100: 254-260.

• Boyko, A.R., S.A. Brooks, A. Behan-Braman, M. Castelhano, E. Corey, K.C. Oliveira, J.E. Swinburne, R.J. Todhunter, Z. Zhang, D.M. Ainsworth and N.E. Robinson, 2014. Genomic analysis establishes correlation between growth and laryngeal neuropathy in Thoroughbreds. BMC Genomics 15: 1-9.

• Dixon, P.M., B.C. McGorum, D.I. Railton, C. Hawe, W.H. Tremaine, K. Pickles and J. McCann, 2001. Laryngeal paralysis: a study of 375 cases in a mixed‐breed population of horses. Equine Vet. J. 33: 452-458.

• Ducharme, N.G. and F. Rossignol, 2019. Chapter 46: Larynx. In: J.A. Auer, J.A. Stick, J.M. Kümmerle and T. Prange. Equine Surgery (Fifth Edition) (pp. 734-769). Elsevier.

• Dupuis, M.-C., Z. Zhang, T. Druet, J.M. Denoix, C. Charlier, P. Lekeux and M. Georges, 2011. Results of a haplotype-based GWAS for recurrent laryngeal neuropathy in the horse. Mamm. Gen. 22: 613-620.

• Garrett, K.S., S.W. Pierce, R.M. Embertson and A.J. Stromberg, 2010. Endoscopic evaluation of arytenoid function and epiglottic structure in Thoroughbred yearlings and association with racing performance at two to four years of age: 2,954 cases (1998–2001). J. Am. Vet. Med. Assoc. 236: 669-673.

• Hawkins, J.F., 2014. Advances in equine upper respiratory surgery. John Wiley & Sons.

• Herdan, C., B. McGivney, K. Gough, E. Hill and L. Katz, 2014. A Single Nucleotide Polymorphism (BIEC2-808543) on Eca3 is associated with Recurrent Laryngeal Neuropathy independent of height in Thoroughbred horses. Equine Vet J. 46: 34.

• Ibi, T., T. Miyake, S. Hobo, H. Oki, N. Ishida and Y. Sasaki, 2003. Estimation of heritability of laryngeal hemiplegia in the Thoroughbred horse by Gibbs sampling. J. Equine Sci. 14: 81-86.

• Miller, S.M., 2020. Endoscopic recurrent laryngeal neuropathy grade prevalence in a sample of thoroughbred yearlings at public auction in South Africa (2013–2019). J. S. Afr. Vet. Assoc. 91: 1-5.

Electroarthrography to Predict Cartilage Quality

Article by Jackie Zions interviewing Dr. Adele Changoor

Researchers from the Ontario Veterinary College (OVC) and University of Toronto are developing a novel method to measure the quality of cartilage in horses using electroarthrography (EAG). EAG is a non-invasive technique that uses electrodes attached to the skin around a joint to detect electrical signals produced by the cartilage when it is loaded.

Dr. Adele Changoor, from the University of Toronto and Lunenfeld Tanenbaum Research Institute, and Ontario Veterinary College researcher Dr. Judith Koenig from the department of Clinical Studies, explain how EAG works and why it may become very useful for predicting cartilage quality and diagnosing osteoarthritis and other degenerative joints diseases in horses.

EAG is analogous to electrocardiography (ECG), which measures the electrical activity of the heart. Cartilage produces electrical signals during loading and these signals reflect its biomechanical properties, such as stiffness and permeability. 

“By measuring EAG signals, we can get an idea of how healthy the cartilage is,” said Changoor.

Healthy cartilage ensures joints can move without pain and has an important role preventing wear and tear on bone.  

Currently, there are no readily available tools to assess cartilage quality in horses with the exception of diagnostic arthroscopy – a minimal invasive surgery – under general anaesthesia. X-rays and ultrasound are not sensitive enough to detect cartilage changes, and magnetic resonance imaging (MRI) is expensive, requires anaesthesia and is often difficult to access. EAG offers a potential alternative that is fast, easy, and affordable.

“EAG is a promising tool for detecting cartilage damage early allowing intervention with treatments that can slow down or prevent further deterioration of the joint,” says Koenig “EAG could also help us monitor the effectiveness of treatments over time.”

EAG measurements were collected at the same time as the centre of pressure (COP), which measures the distribution of force under the horse’s hoof when it stands or walks. 

“EAG is really tied directly to cartilage biomechanical properties,” says Changoor.   “We also needed to know about the joint biomechanics in order to interpret EAG properly.”  A custom, portable, force mat was developed by Dr. Changoor’s graduate students that included an array of force sensors to place under the horse’s hoof when measuring EAG. 

“Then we can measure how much compressive force or ground reaction force is being exerted on that joint”, said Changoor.  “COP, is where the ground reaction force is acting.  The ground reaction force gives us the total load on the joint.  COP lets us figure out where on the hoof or where on the joint surface force is being concentrated.”

COP provides information about the joint biomechanics and the horse’s balance and stability.  EAG and COP testing were combined to get a comprehensive picture of the joint health and function in horses with osteoarthritis.  Results were compared with MRI imaging and it was found that EAG and COP testing correlated well with MRI and could detect differences in cartilage quality between healthy and osteoarthritic joints.

In the 2023 study involving horses with osteoarthritis in the fetlock joint; the horses were treated with MSCs to decrease inflammation and stimulate tissue healing. The researchers measured EAG, COP, and MRI before and after the treatment to evaluate its impact on cartilage quality.

“We observed that MSCs improved cartilage quality in some horses and EAG and COP testing were able to capture these changes and show the responses to treatment. This suggests that EAG and COP testing could be useful for selecting treatment options for the horse,” says Dr. Koenig.  “One of the biggest advantages of EAG is that it seems to correspond with our arthroscopic findings. It can perhaps evaluate the quality of the cartilage or cartilage defects, which we are at the moment only able to evaluate with arthroscopy.”

The researchers plan to conduct further studies in order to validate and refine EAG and COP testing for predicting cartilage quality in equines. They hope that these techniques will become widely available and accessible for veterinarians and horse owners in the future.

“This is an exciting and innovative research project that has the potential to improve the diagnosis and early management of osteoarthritis in horses,” says Dr. Koenig  “Osteoarthritis is a major health and welfare issue for horses and their owners, and we need better tools to detect it early and treat it. EAG and COP testing could provide a simple, affordable, and accurate way to assess cartilage quality and joint function in horses.”

Assessing the approaches to diagnosing and treating proximal suspensory desmitis

Article by Connor Parsons DipWCF

Diagnosing proximal suspensory desmitis in the hind limb can be difficult. However, the modern diagnostic modalities available to the industry today makes it possible to isolate injuries, allowing both veterinarians and farriers to work together to achieve the best diagnosis and prognosis possible for the equine in question.

In this article, Connor Parsons reviews the anatomy and function of the suspensory ligament, causes and signs of proximal suspensory desmitis and whether there is an ideal procedure for diagnosing, treating and formulating a prognosis for the horse as part of his DipHE Farriery studies. 

ANATOMY

The equine limb is complex yet effective. The suspensory ligament is made up of dense white fibrous connective tissue which suspends the fetlock and prevents hyperextension.

Originating at the proximal, plantar aspect of the third metatarsal/carpal attaching to two palmar depressions distal to the carpometacarpal and tarsometatarsal joints descending the channel formed by the 2nd, 3rd and 4th metatarsal/carpal, bifurcating two thirds of the way down the 3rd metatarsal/carpal, making a firm attachment to the palmar aspect of the proximal sesamoids, pulling the sesamoids proximally, then travelling dorsally and distally at an oblique angle to merge with the common digital extensor tendon. This forms a sling to support the fetlock joint. The ligament and its branches are strong but only slightly elastic (Devereux, 2006).

The suspensory ligament also forms a part of the hindlimb stay apparatus which is a system of ligaments, tendons and muscles that work together to allow the horse to stand and doze with minimal muscular effort. Also known as the fright and flight mechanism (Colles & Ware, 2020).

DAMAGE TO THE SUSPENSORY LIGAMENT

Suspensory ligament damage can affect horses of all breeds and ages. However, it is most common in competition horses. Proximal suspensory desmitis (PSD) is inflammation or damage of the main body at the origin of the ligament at the proximal end of the third metacarpal/metatarsal.

The suspensory ligament can be inflamed or there can be changes to the fibre pattern of the ligament. These cases will present with lack of performance, being worse on soft surfaces. In more severe cases a core lesion (hole) can be seen on an ultrasound scan, where a number of fibres have ruptured. This type of injury will have a more sudden onset of lameness (Dyson, 1994). Injury can be solely within the ligament, involve tearing of the fibres of the ligament or be connected to avulsion fractures at the origin, involving the proximal 3rd metacarpal/tarsal (Baxter, 2020). Complete rupture is possible, however, very rare. The prognosis for a complete rupture is not favourable (Dyson, 1994).

Although the suspensory ligament has a slight elasticity to its make-up, if it is stretched it tends to heal with a loss of elasticity making it susceptible to recurrent damage (Colles & Ware, 2020).

SIGNS OF PROXIMAL SUSPENSORY DESMITIS

Proximal suspensory desmitis is a difficult condition to diagnose as the hind limb is complex and many of the functioning structures work in unison. A horse suffering with inflammation or damage to the main body of its hind suspensory can present one of three ways. It may have a unilateral lameness, a bilateral lameness or just a general decrease in performance (Dyson,1994).

CAUSES OF PROXIMAL SUSPENSORY DESMITIS OF THE HINDLIMB

Although there has been extensive research into proximal suspensory desmitis, there is no primary cause in all cases. 

Proximal suspensory desmitis is a common injury in both front and hind limbs of the equine athlete. Usually bilateral in the hind limb (Dyson, 2016). All types and breeds of horses are susceptible to this type of injury. Poor conformation is a contributing factor to proximal suspensory desmitis.

Conformational defects such as straight hocks, sloping pasterns and long-toe, low-heel conformations would be at higher risk to injury. These conformational defects will all apply unnecessary pressure to the suspensory ligament. Horses that have suffered with this condition will be predisposed to a repetitive strain injury of this ligament (Devereux, 2006). Overextension of the tarsus as a result of overextension of the fetlock has been linked to proximal lesions. The higher the severity of trauma, the higher the severity of ligamentous lesion. Working horses on deep, soft surfaces will increase the risk of this injury (Baxter, 2020).

The hindlimbs are more frequently affected with this condition than the forelimbs with a much lower success rate of the horse returning back to performance prior to rest (69% hind vs 80% forelimb) (Colles & Ware, 2020).

DISCUSSION

In a study of six horses, this is an extremely small cohort of horses to be able to state an average age a horse is likely to present with this condition. This study also shows that all of the horses studied were of varying fitness levels, therefore stating that this does not affect the likelihood of injuring the hind suspensory ligament. There was only one horse in this study that was unfit and overweight. The rest were all competition fit with good muscle mass, showing that fitness doesn’t necessarily decrease the risk of this injury happening. The case history of the six horses studied did not include which discipline or level the horse was working at. This would be an interesting factor to consider when looking at which horses would be more susceptible to proximal suspensory desmitis.

Each individual case was being looked after by different veterinarians, giving a clear picture of different approaches on how to diagnose and treat this condition. Although for the purpose of a study the varying opinions will make the comparison more difficult. All horses presented with a reduction in performance prior to veterinary contact. Only one horse was reported with a bilateral lameness behind. Flexion testing appeared to aggravate the lameness making it more prominent to see. Local analgesia has been shown to be effective in isolating the area to be investigated. Also, showing lameness on the other hind once the worse limb has been blocked out.

Using digital diagnostic modalities such as ultrasonography to diagnose this condition allows the veterinarian to study the changes in the fibre pattern of the suspensory ligament. This will allow the veterinarian to see the severity of damage caused and allow them to provide the best treatment plan possible. In this study only one horse had a lesion while the other five horses had thickening and slight changes to the fibre pattern. Horse 2 had lesions on both hind limbs however the veterinarian didn’t medicate, box rest was recommended. His prognosis was guarded.

Although radiographs of the feet don’t directly help with the diagnosis of proximal suspensory desmitis, they do allow the farrier to trim accordingly to restore the hoof back to correct hoof pastern axis and mediolateral foot balance. This will reduce lever arm forces thus reducing any unnecessary pressures on the plantar aspect of the limb.

Horses were radiographed for foot balance to aid with remedial trimming and shoeing. This will increase the equines prognosis allowing the farrier to have a clear picture of what is being dealt with. All of the horses that were radiographed presented with a negative sole plane and weak heels.

The question is whether this foot conformation is because the horses are wanting to apply more pressure to the caudal aspect of the hoof in the landing phase, reducing the movement of the metacarpophalangeal articulation. This is an attempt to reduce the loading forces applied to the suspensory ligament. However, it will also cause the heels to become weak. Or, if this conformational defect has caused the suspensory ligament to become inflamed or damaged, thus causing proximal suspensory desmitis.

Proximal suspensory desmitis can be secondary to other conditions such as hock conditions or sacroiliac problems which cause the horse to adopt a different gate. Therefore causing unnecessary loading on the suspensory ligament. It is important that the primary cause is diagnosed and treated when treating proximal suspensory desmitis. This is where scintigraphy can be a useful tool to get a clear picture of the cause involved in individual cases. Scintigraphy is an expensive diagnostic modality which carries significant health and safety risks, this must be taken into consideration when dealing with cases.

All horses studied were worse on a soft surface where it is harder for the horse to guard itself from soft tissue injuries. Horses that are worse on soft surfaces generally are suffering from soft tissue pain. However, nerve blocks will help the veterinarian pinpoint the structures involved when diagnosing lameness.

Although it is possible to have a unilateral lameness with proximal suspensory desmitis in the hind limb it is most common for the lameness to be bilateral. All of the horses in this study had a bilateral lameness, generally worse on one limb than the other. Although presenting prior to veterinary contact as lack of power or struggling to strike off on the correct canter lead.

When a veterinarian is deciding on a treatment plan, the horse is looked at carefully including its previous history as some treatments come with higher risks, although can be extremely effective for reducing inflammation. Shockwave treatment comes with minimal risks involved and is effective; however, many racing authorities require a mandatory 5 day Stand-Down period from racing following the administration of extra-corporeal shockwave therapy. Findings from this study show that the horses with the best prognosis of getting back to competitive work have undergone surgery. Understandably this is the last resort treatment as it is invasive and expensive for the client. 

Only one horse from this study did not have any medical intervention and this horse had the least favourable prognosis. This would suggest that box rest alone is not generally enough if the horse is expected to get back to full athletic fitness. The most common veterinary treatment is steroidal injections into the area of interest and shockwave therapy with rest. However, the use of corticosteroids in horses in training often adopt a clear 14-day exclusion on the use of intra-articular (joint) injections before racing in line with different racing authority regulations.

Water based therapy can also be considered as part of the recovery process when bringing the horse back into work. It’s known to reduce limb oedema, stimulate nerves, and improve circulation, which speeds the healing process and provides pain relief. It also aids in joint stability, providing all-around support to the limbs. 

Cold water therapy is typically prescribed when the goal is to reduce heat and inflammation. Applying cold water or ice reduces the amount of accumulating fluid to an injured area and can somewhat numb the area, causing a topical analgesic effect. 

Underwater treadmills are often used for horses with tendon and ligament injuries to provide a gradual transition back into exercise and regain the range of motion. Swimming is also used to condition the horse without putting a load on the skeletal system. It is often used in the early stages of tendon and suspensory injuries due to no pressure being placed on the lower limb. Trainers who use swimming as part of their routine often find that, in addition to the cardiovascular workout, it also helps the horse relax and settle its mind.

This is not always successful and horses are then admitted for surgery. While the surgery for this condition is successful, there must be consideration taken into the fact that it is not legal to compete at certain levels once this surgery has taken place.

The study shows that the farriery treatment involved when dealing with this condition is varied, depending on which veterinarian the horse is being looked after by. However, the author has had positive results from many different shoeing styles. The main importance of trimming and shoeing for this condition has been shown to restore the best possible hoof pastern axis through trimming, supporting the entire limb and fitting a shoe with an early breakover. This will reduce the lever arm on the metacarpophalangeal articulation, thus minimising unnecessary pressure on the suspensory ligament.

CONCLUSION

Having such a small cohort of horses in a study makes it difficult to finish with a conclusive result. This small study however, has given a positive result in the diagnosis stages of dealing with this condition. At this stage nerve blocks are invaluable along with ultrasonography. In less obvious cases MRI is useful to gain a diagnosis and occasionally scintigraphy will be used to locate the problem. Radiography is a useful tool when dealing with PSD and checking the origin area for avulsion fractures.

This study has also shown that there is a link between a negative solar angle and proximal suspensory desmitis. However, this would need to be studied further and on a greater scale to determine why there is a link between this conformational defect and this condition.

It is paramount that correct foot balance is achieved by the farrier. To achieve this foot balance radiographs are required. This study has shown that there is no definitive way to shoe for this condition, however it has shown a positive result from an early breakover shoe, allowing the horse relieve pressures on the caudal aspect of its hoof. Horses that had the best prognosis underwent surgery, allowing them to get back to competitive fitness.

REFERENCES

Baxter, G. M., 2020. Adams and Stashak's Lameness in Horses. 7th Edition ed. Hoboken, NJ: John Wiley & Sons.

Colles, C. & Ware, R., 2020. The Principles of Farriery. 2nd edition ed. Marlborough: J.A.Allen. 

Devereux, S., 2006. The Veterinary Care Of The Horse. 2nd Edition ed. London: J.A.Allen. Dyson, S., 1994. Proximal suspensory desmitis in the hindlimb: 42 cases. British Veterinary Journal, 150(3), pp. 279-291.

Dyson, S., 2016. American Association of Equine Practitioners. [Online] Available at: https://aaep.org/horsehealth/lowdown-high-suspensory-disease-proximal-Suspensory-desmitis [Accessed 19 11 2022].

Smith, M., 2022. Newmarket Equine Hospital. [Online] Available at: https://www.newmarketequinehospital.com/media/pm1beabc/hah349-Vet_susp_desmitis-final.pdf [Accessed 9 April 2023].

There's more to it than meets the eye!

Article by Adam Jackson MRCVS

The horse’s eyesight has evolved to scan its environment rather than picking up sharp details, in order to survive from predators.  As a prey animal, the horse’s eyes are eight times larger than a human’s eye; however, this makes them more vulnerable to injury and disease that may be catastrophic.  Horses develop many of the same eye problems as humans such as glaucoma, corneal ulcers, cataracts and other issues.   

The working of the eye 

Vision is provided by light entering the eye, which is made into an image by the brain through various complex biomechanical and physical processes.  

As light enters the eye, it is targeted to the retina by the cornea and the lens bending the light.  This light reaches the sensory tissue at the back of the eye.  In fact, the retina or nervous tunic is made of cells that are extensions of the brain coming off the optic nerve.  The retina consists of 2 types of photoreceptors called rods and cones.  The rod cells are more light-sensitive, thus providing night vision, whereas the cones are less light sensitive but provide visual acuity and the ability to see colour.  The optic disc in the retina does not contain photoreceptors and is the location the optic nerve leaves the eye to transmit the visual information to the visual cortex of the brain.   

Visual field of the horse 

Because the horse’s eyes are positioned on the side of the head, the range of vision is roughly 350 degrees, thus, allowing the horse to spot potential predators.  Due to the positioning of the eyes, the horse has two blind spots that include in front of the face and behind its head extending over its back and behind the tail.   

The horse has both binocular and monocular vision. Monocular vision means vision in one eye only and binocular vision means seeing with two eyes.  65 degrees of the 350 degree vision consists of binocular vision while the remaining 285 degrees is monocular vision.  As a result, the horse has a smaller field of depth perception compared to a human.  The horse must raise or lower its head in order to increase its range of binocular vision.  By introducing a bit and making the horse hold its head perpendicular to the ground, the binocular vision becomes less focused on distant objects and more focused on what is immediately in front of the horse.  Show jumpers and jump jockeys allow the horse to raise its head a few strides before a jump so that the horse can properly assess the jumps to allow appropriate take-off. 

Sensitivity to light 

Horses’ eyes have evolved to allow them to have good vision in dim light and due to this evolution they have better vision on slightly cloudy days compared to sunny, bright days.  There are two particular structures that allow them to have superior night vision, which include a high proportion of rods to cones (20:1) and the presence of the tapetum lucid.   

The horse’s large pupils allow a large amount of light to enter and the size of the retina allows a high number of cells to be involved in the capturing of light. In addition to the rods and cones, the horse's tapetum lucidum is a reflective structure in the back of the eye that bounces light back to the photoreceptors for a second time, thus further increasing the ability to capture more light.  Ultimately, this structure allows greater night vision.   

Interestingly, horses have also evolved structures to protect their eyes from photic damage during bright sunny days.  The pupil has the ability to significantly constrict in order to reduce the amount of light entering the eye.  In addition, there is a structure referred to as the corpora nigra, which is a bulbous structure extending from the iris into the space of the pupil that acts as a shade.    

Colour Vision 

Horses have dichromatic vision; therefore, they are not colour blind but they have a smaller spectrum than humans typically do.  Horse’s dichromatic vision means they see in the green-blue spectrum and the ocular variations based upon them.  They cannot distinguish red and are often thought to have a red-green colour blindness.  The horse’s colour vision must be taken into account when designing obstacles for horses to jump.   

Eyelids 

There are three layers to the eyelids that include a thin layer of skin covered in hair, a layer of muscles that allow the opening and closing of the eyelid and the palpebral conjunctiva, which lies against the eyeball.  The horse also has a third eyelid, also known as the nictitating membrane which has the function of protecting the cornea.   

Non-pigmented third eyelids are more susceptible both to solar-induced inflammation and to squamous cell carcinoma. Therefore, careful scrutiny of this structure is important.  Prominence of the third eyelid may be a result of inflammation caused by solar-induced inflammation or conjunctivitis (inflammation of the conjunctiva).  Inflammation and neoplasia should be differentiated on the basis of clinical appearance.  For example, squamous cell carcinoma has a plaque-like appearance and erosion. Conjunctivitis is the inflammation with thickening and reddening of the transparent membrane that lines the eyelid and eyeball.  Any suspected tumour should be excised and undergo histopathology to determine if it is indeed neoplasia or a type of inflammation.  Other neoplasia that may occur in the eyelids are melanomas or periocular sarcoids.   

Entropion is the inversion of the eyelid margin and lashes.  Often seen in foals as a consequence of either anatomical imperfection or of dehydration and debility, it is the inward rotation of the eyelid that leads to the rubbing of hair in the cornea leading to keratitis.  Later onset entropic is usually a consequence of a traumatic injury and can result if primary repair of an eyelid laceration has not been performed.   

Trauma to the eyelids may result in bruising or a laceration.  If bruising has occurred, a warm compress may be helpful if the horse will tolerate it.  If a laceration has occurred it should always be repaired. 

Lacrimal system  

The horse has a pair of nasolacrimal ducts that carry lacrimal secretions, commonly known as tears, from the eye to the nasal cavity.   

Keratoconjunctivitis sicca is a deficiency in the acqueous portion of the tear film and is relatively rare.  If it occurs, it is a result of damage to the facial nerves or direct damage to the lacrimal gland or duct. With the lack of tears the cornea appears dull and lacklustre and may lead to corneal ulceration.  It is often associated with a mucopurulent eye discharge as well as pain and inflammation.  This condition can be managed with regular cleaning and the application of a tear replacement solution.  

Acquired stenosis/occlusion of the lacrimal drainage system may be a consequence of infectious, trauma, neoplastic or inflammatory disease within the drainage system or external to it. It is often presented with epiphora (tear overflow) or a mucopurulent discharge if infection is involved.  Following treatment of the underlying cause, the goal is to re-establish the drainage system with flushing of the duct with saline solution, or a combination of steroid, antibiotic (if required) and saline solution.  

Conjunctiva/Sclera 

The sclera is the white of the eye which is the relatively tough outer layer of the eye and is covered by a thin mucous membrane, referred to as the conjunctiva, and runs from the edge of the cornea and covers the inside of the eyelid.  

Conjunctivitis is the inflammation and swelling of the conjunctiva and includes a primary conjunctivitis or a secondary conjunctivitis.  Primary conjunctivitis is inflammation caused directly by irritants, chemicals, toxins and bacteria.  However, conjunctivitis may be secondary to another ocular disease such as disorders of the lacrimal system, eyelid problems, and keratitis.  In addition, conjunctivitis may be a non-specific symptom of other systemic diseases such as a respiratory viral infection.  Conjunctivitis presents with a reddened inflamed conjunctiva with mould, purulent, serous or a combination of these discharges.  The horse will have discomfort of the eye with this ailment.   

Conjunctival foreign bodies are often acute and unilateral and caused by organic material resulting in excessive tearing, inflammation of the conjunctiva and ocular discomfort.   

Conjunctival neoplasia is most often a squamous cell carcinoma (SCC) as this tumour usually affects areas of epithelial transition such as the mucocutaneous junction of the eyelids.  The extent and appearance of the lesion is variable but SCC should always be considered especially in those horses lacking pigment in those areas. The symptoms range from mild ocular discomfort with discharge to plaque-like and cauliflower-like masses without ulceration.   

Cornea 

The cornea is the transparent front part of the eye that covers the iris, pupil and anterior chamber.  It is a domed-shaped structure that acts as the eye’s windshield protecting the eye from insult such as an infection.  Along with the tear film, it provides a proper anterior refractive surface for the eye, in fact, it contributes two-thirds of the refractive power of the eye.  Congenital problems of clinical significance are rare in horses but acquired corneal problems as a result of trauma are common in horses. 

Traumatic keratitis due to lacerations or penetrating injuries are common and in most cases involve full thickness penetration, acqueous loss and iris prolapse.  This condition presents with sudden and severe pain accompanied with excess tearing and blepharospasm (involuntary tight closure of the eyelids).  The extent of the damage to the cornea can be determined by the use of fluorescein dye.  If the wound is not repaired quickly then the iris may become incarcerated and the restoration of the normal eye anatomy is difficult.  

Abrasions to the surface of the cornea is a common condition seen by equine practitioners.  Some simple scratches heal quickly while others may become more complex, involving fungal or bacterial infections resulting in a protracted recovery. 

Corneal ulcers are a defect in the surface of the epithelium of the cornea that involves the underlying stroma.  They are often described as sores on the cornea.  It is important that they are diagnosed and treated promptly as there is potential that the horse’s vision may be affected. The clinical symptoms are often ocular discomfort with excessive tearing, squinting or blepharospasms. Discolouration and swelling of the cornea and the eventual development of blood vessels around the ulcer and an irregularity of the cornea. The depth of the ulcer must be established and it may range from superficial to deep.   

Liquefactive stromal necrosis (melting ulcers) are not an uncommon condition in the horse and may present acutely or as a progression from a corneal ulcer.  It should be deemed as an emergency because corneal perforation may result.  This disease may be accompanied by uveitis.   

Corneal foreign bodies are usually organic material and present with blepharospasm, excess tearing and pain.  Various illuminations, magnifications as ophthalmic stains may be used to identify it and aid in removal.  

Bacterial keratitis is often seen after a corneal injury especially if an ulcer is present. The horse will demonstrate acute eye pain with serous discharge that quickly becomes mucopurulent or purulent.  The clinical appearance is not usually diagnostic and cultures and scrapings should be taken from the edge of the ulcer. This procedure ensures the correct selection of treatment and pain relief.  

Mycotic keratitis is uncommon in the UK but with the changing climate it may become more prominent.  This type of keratitis is a result of fungal growth so tends to occur in climates supportive of this type of growth. Diagnosis is based on the history, clinical appearance and the demonstration of fungal hyphae and positive fungal culture. This disease may be a consequence of inappropriate drug therapy (such as corticosteroids) or from previous corneal trauma. Following the identification of the fungus, topical treatments can be used but may take weeks to months.  

Uveal Tract  

The uveal tract consists of three parts that include; The choroid which is the tissue layer filled with blood vessels; The ciliary body that is the ring of tissue containing muscles that change the shape of the lens as well as producing the clear fluid that fills the space between the cornea and the iris; The iris which is the coloured part of the eye.   

Persistent pupillary membranes are vascular arcades and developing tissue of the eye that fail to atrophy as the eye matures.  These are very common in horses and usually have no consequence and no treatment is needed.  

Cysts may arise in various parts of the uveal tract and are not uncommon in the horse.  Irrespective of their origin, they may vary between pigmented to unpigmented and are smooth, round and do not invade neighbouring tissue. No treatment is required except on rare occasions when they interfere with the horse’s vision.  

Neoplasia of the uvea is not common but may arise and are often melanomas that are locally invasive but without cellular malignancy. 

Trauma of the iris may result from direct trauma, or a secondary consequence of corneal perforation or a whiplash injury.  Any uveitis that is caused by trauma can be treated medically.  If there is an iris prolapse, then the iris is placed back into the anterior chamber provided they are not contaminated. Any foreign bodies must be removed and any hyphaema (bleeding in the anterior chamber between the cornea and iris) is usually left to be resorbed naturally. 

Uveitis is inflammation of the uveal tract and can cause eye pain and alterations in vision. There are many causes of uveitis that include trauma, lens-associated uveitis, general viral infections (such as equine viral arteritis) and bacterial disease (such as Rhodococcus equi in foals).  However, many situations of uveitis are an immune-mediated uveitis often referred to as equine recurrent uveitis (also known as moon blindness). Uveitis may present as an acute or a chronic condition. 

This disease can be treated medically often with the use of a sub-palpebral or nasolacrimal lavage system.  In addition, the patient should be placed in a quiet fly-free and dust-free environment.  

Lens 

The lens is a clear curved disk that sits behind the iris and in front of the vitreous of the eye, which bends light as it enters the eye to develop an image.  The horse’s lens is large and minor opacities associated with embryonic remnants are common.  

Cataracts are the most common lens abnormality to be encountered causing an opacity of the lens.  Cataracts may be acquired from trauma or post-inflammation situations.  However, cataracts may be congenital commonly seen in Arab and thoroughbred foals.   These opacities can be classified in various ways: 

Age of onset – juvenile, senile or congenital 

Cause - post inflammation (uveitis) or trauma   

Location – cortical, capsular, nuclear, polar, equatorial 

Stage of development – immature, mature, hypermature

Most cataracts cause no obvious visual deficits unless they are dense and obstruct the visual axis.  in which cataract surgery may be considered.  

Acqueous drainage 

The acqueous humor is a transparent water-like fluid similar to blood plasma but containing low protein levels. It is secreted from the ciliary body (a supporting structure of the lens) and fills both the anterior and posterior chamber of the eye.  

Glaucoma is a pathological elevation of the intraocular pressure resulting in the optic nerve becoming damaged . Primary glaucoma in horses is exceptionally rare while secondary glaucoma is uncommon but may occur after anterior segmental inflammation. Often there is little to no pain but an enlarged globe and raised intraocular pressure with the lack of pupillary light reflex may be seen.  Treatment may be attempted if the vision is present with various medications to reduce the intraocular pressure.  If the horse is blind it may be left without treatment. 

Conclusion

Good eye care is vital as the horse relies on its site to receive a great deal of information on its surrounding environment.  Even with the horse holding its head forward it has remarkable peripheral vision but the horse’s vision is a little blurrier and less colourful compared to humans.  In addition, both the strengths and weaknesses of the visual abilities of the horse must be seriously considered when looking at various techniques for training. 

Gut issue biomarkers and their use in signalling dysbiosis

Article by Jackie Zions

Gastrointestinal issues (GI) are the number one cause of morbidity in horses other than old age.   An unhealthy digestive system can cause poor performance, pain, discomfort, diarrhoea, and a whole host of issues that can sideline your horse.  It’s no wonder researchers are paying close attention to the ‘second brain’ and its billions of inhabitants.  Ontario Veterinary College (OVC) researcher, Dr. Luis Arroyo has been studying the equine gastrointestinal systems for many years with several research projects receiving funding from Equine Guelph.  Arroyo discusses what we know about equine gut health, causes of GI disorders and the extensive continuing research to understand what unstable and stable gut populations look like.

Starting with some basic anatomy Arroyo says, “The gastrointestinal tract of a horse is extremely large, and there are many things that can cause disturbances to the normal functioning or health of the gut.”  A healthy gut microbiome is essential for the horse’s entire body to function optimally.

Signs of GI issues

Common signs of disorders could include abdominal pain, bloating, changes in faecal consistency (including diarrhoea or constipation), excessive drooling, decrease in water consumption, lack of or poor appetite, weight loss and low body condition score.  

“Some cases are more obvious to owners,” says Arroyo, “like poor performance, or acute or chronic diarrhoea.” 

Changes of behaviour such as becoming cranky or moody can be tell-tale signs there is unrest in the GI system.  Biting at the flanks can signal abdominal pain as well as reactivity to being saddled.  When the horse stops wanting to perform and athletic abilities suddenly decline, if there is no obvious lameness, GI issues are high among the considerations.

“Horses are herbivores, designed to consume a diet of forage, and to break down complex sugars within that forage.” says Arroyo.  “The gut microbiota does this job and is very important for healthy digestion.”  Recent research is connecting the changes in diversity of microbial communities to conditions like colic, colitis, and gastric ulcers.

Causes of GI Issues

Colic is the number one clinical condition occurring in horses.  It is well-known that sudden dietary changes can be a major contributor as well as diets that are high in grain.  This can create changes in the volatile fatty acids produced in the GI system, which in turn can lead to the development of gas colic.  Arroyo provides the example of switching from dry hay fed in the winter, to rich, lush, spring grass as a big cause of rapid fermentation that can cause colic.  

Any abrupt change, even if it’s a good quality feed to a different good quality feed, can be a source of colic.  Then there is the more obvious consumption of mouldy, poor quality hay.  So not only the quality but the transition/adaptation period needs to be considered when making feed changes and this goes for both changes to forage or concentrates.

A table of feed transition periods on the Equine Guelph website states an adaptation period of at least 10 – 14 days is recommended.  Transition periods under seven days can increase colic risk over 22 times!  (https://www.equineguelph.ca/pdf/tools/How%20to%20Transition%20Feedstuff.pdf)

“Decrease in water consumption can be an issue, especially in countries with seasons,” says Arroyo.  When water gets really cold, horses often drink less, and if it freezes, they don’t drink at all, which can lead to impaction colic.   Parasite burden can also cause colic. If your horse lives in a sandy environment, like California, ingesting sand can cause impaction colic.  

Non-steroidal anti-inflammatory drugs (NSAIDS) can cause colic or ulcers. NSAIDS can interfere with blood supply to the GI tract causing ulceration, for example in the mucosa of the stomach. Prolonged use can cause quite severe ulceration.

NSAIDS are not the only drugs that can contribute to GI issues.  “Antibiotics - as the name says - kill many kinds of bacteria,” says Arroyo. “They are designed for that!  Invariably they deplete some bacterial populations including in the intestine, and that is a problem because that may allow some other bacteria, potentially pathogenic or harmful, to overgrow, and that can cause dysbiosis.”  
In a recent study, by fellow OVC researcher, Dr. Gomez and co-workers, it was determined that damage to the intestinal microbiota could occur after only 5 days of administering antibiotics to horses.  Damage to the intestinal microbiota resembled dysbiosis that can potentially result in intestinal inflammation and colitis predisposing the horse to diarrhoea.  Judicious use of antibiotics and antimicrobials are advised.

There are infectious and non-infectious causes of colitis.  Infectious examples include salmonella and then there is Neorickettsia risticii, which if ingested from contaminated sources, can cause Salmonellosis or Potomac horse fever, respectively.

“Any stress factors such as transportation, fasting or intense exercise like racing, can be a factor for developing stomach ulcers,” says Arroyo.  

Current Diagnostics

Putting together a picture of the horse’s health status includes gathering clinical history from the horse owner and performing a physical examination for motility and hydration status. A biochemistry profile and complete set count can be gathered from blood testing.

Gastric ultrasound allows veterinarians to view the wall of the intestine, noting if it has thickened or distended, which could occur in cases when there is colic.  They can assess appearance and find out if the intestine is displaced or if there is a twist.  Gastroscopy is commonly used to find ulcers in the stomach and can reach as far as the first part of the duodenum. 

GI Research

“DNA sequencing has been a breakthrough in science in terms of understanding the communities of different microorganisms living in many different niches from the skin to the lungs to the upper airways to the intestine,”  says Arroyo.

It has allowed in-depth study of the population of microorganisms, providing a big picture of the different inhabitants in various areas of the GI tract, such as the lumen of the small intestine and the small and large colon.  “The microorganisms vary, and they have different functions in each compartment,” says Arroyo.  

DNA sequencing has allowed researchers to study microbial populations and gather information on what happens to bacterial communities when impacted by diseases like colitis.  “We can see who is down, and who is up,” explains Arroyo, “and determine what populations have been depleted.”  It has led to a better knowledge of which of the billions of factors are harmful to the system and which can compromise the health of the horse.

Robo-gut is one example of a fantastic system where bacterial communities are being replicated in the lab to mimic what would be found in a natural environment.  

Researchers at the University of Guelph have measured metabolic profiles of the bacterial population after the addition of supplements like probiotics and prebiotics.  They found they can dramatically change the metabolites that are being produced, according to what is being added to the system.

Exciting new research that could impact the future of diagnostics includes screening for biomarkers as indicators of intestinal health among equine microbiota.  Dr. Arroyo is currently working with research partner, Dr. Marcio Costa, from the University of Montreal, looking for biomarkers that indicate changes in the inhabitants of the equine gut that take place during the early onset of illness.

“A biomarker is a biological molecule that you can find in different places,” explains Arroyo.  “For example, you might find them in tissue, blood, urine, or different body fluids.  They can signal normal or abnormal processes or could reveal a marker of a disease.  For example, a biomarker can be used to see how well the body might respond to a treatment or to a disease condition.”

“The objective of a dysbiosis index is quantifying ‘X’ number of certain bacteria that are important to us,” says Arroyo.  In this case, the dysbiosis derives from sequencing of the bacterial population in faecal samples.  

Changes in the intestinal microbiota (dysbiosis) are present before and during the outset of diseases and after treatment with antibiotics.  Arroyo cites the example of decreased Lachnospiraceae commonly observed when there is intestinal inflammation.  

Bacterial biomarkers are currently being used in other species to accurately predict intestinal dysbiosis, for example in cats and dogs.  One canine study quantified the number of seven different taxa of importance of the total bacterial populations.  This information is entered into a mathematical algorithm that comes up with results explaining which bacteria have increased or decreased.  Based on those numbers, one can use a more specific taxa to identify dysbiosis.  In a feline study, it was discovered that six bacterial taxa could be accurately used to predict diarrhoea in 83% of cases.

It is hoped the same results could be accomplished for horses.  Developing PCR testing to screen for biomarkers could be a game changer that could potentially provide speedy, economical early diagnostics and early treatment.

So far, the most remarkable finding in the preliminary data reveals that in horses with colitis, the whole bacterial population is very depleted.

“At this stage we are in the process of increasing our numbers to find significant differences in which bacterial taxa are more important,” says Arroyo.  “Soon we hope to share which bacteria taxa are more promising for predicting dysbiosis in horses with gastrointestinal disease.”

The researchers are delving into a huge biobank of samples to identify potential markers of intestinal dysbiosis in horses, utilising PCR testing as a faster and more economical alternative to the complex DNA sequencing technologies that have been used to characterise changes in microbiota thus far.  The goal is to develop simple and reliable testing that veterinarians can take right to the barn that will result in early treatment and allow closer monitoring of horses at the first onset of GI disease.

Top Tips to Protect Digestive Health

1. Horses are hind gut fermenters who rely on adequate amounts of fibre in the diet to maintain healthy gut function.

2. Make dietary changes slowly as abrupt changes disrupt the microbiota.

3. Avoid large grain meals as huge portions of highly fermentable diets can be quite harmful to the microbiota and can also be a source of risk for developing gastric ulcers.  Opt to spread out concentrates into several smaller rations.

4. Prevent long periods of fasting which can also lead to ulcers.  Horses are continuous-grazers, and they need to have small amounts of feed working through their digestive system to keep it functioning optimally.

5. Have a parasite prevention programme.

6. Provide fresh water 24/7 to maintain good hydration and keep contents moving smoothly through the GI tract.

7. Keep up to date on dental appointments. 

8. Motion is lotion – turn out and exercise are extremely important to gut function.
   

In closing, Arroyo states, “These top tips will help keep the horse happy and the gastrointestinal tract functioning properly.”

The importance of good hoof balance to improve performance

The equine foot is a unique structure and a remarkable feat of natural engineering that follows the laws of biomechanics in order to efficiently and effectively disperse concussional forces that occur during the locomotion of the horse.  Hoof balance has been a term used by veterinarians and farriers to describe the ideal conformation, size and shape of the hoof relative to the limb.  

Before horses were domesticated, they evolved and adapted to survive without any human intervention. With respect to their hoof maintenance, excess hoof growth was worn away due to the varied terrain in their habitat.  No trimming and shoeing were required as the hoof was kept at a healthy length.

With the domestication of the horse and our continued breeding to achieve satisfactory performance and temperament, the need to manage the horse’s hoof became essential in order to ensure soundness and performance.  The horse’s foot has evolved to ensure the health and soundness of the horse; therefore, every structure of the foot has an essential role and purpose. A strong working knowledge of the biology and biomechanics of the horse’s foot is essential for the veterinarian and farrier to implement appropriate farriery.  It was soon concluded that a well-balanced foot, which entails symmetry in shape and size, is essential to achieve a sound and healthy horse.  

Anatomy and function of the foot

The equine foot is extremely complex and consists of many parts that work simultaneously allowing the horse to be sound and cope with the various terrains and disciplines.    Considering the size and weight of the horse relative to the size of the hoof, it is remarkable what nature has engineered.  Being a small structure, the hooves can support so much weight and endure a great deal of force.  At walk, the horse places ½ of its body weight through its limbs and 2 ½ its weight when galloping.  The structure of the equine foot provides protection, weight bearing, traction, and concussional absorption.  Well-balanced feet efficiently and effectively use all of the structures of the foot to disperse the forces of locomotion. In order to keep those feet healthy for a sound horse, understanding the anatomy is paramount.   

The foot consists of the distal end of the second phalanx (short pastern), the distal phalanx (pedal bone, coffin bone) and the navicular bone.  The distal interphalangeal joint (coffin joint) is found between the pedal and short pastern bone and includes the navicular bone with the deep digital flexor tendon supporting this joint.  This coffin joint is the centre of articulation over which the entire limb rotates.  The navicular bone and bursa sits behind the coffin bone and is stabilised by multiple small ligaments. The navicular bone allows the deep digital flexor tendon to run smoothly and change direction in order to insert into the coffin bone.   The navicular bursa is a fluid-filled sac that sits between the navicular bone and the deep digital flexor tendon.

The hoof complex can be divided into the epidermal weight-bearing structures that include the sole, frog, heel, bulbs, bars, and hoof wall and the anti-concussive structures that include the digital cushion, lamina, deep digital flexor tendons, and ungual (lateral) cartilage.  The hoof wall encloses the dermal structures with its thickest part at the toe that decreases in thickness as it approaches the heel.  The hoof wall is composed of viscoelastic material that allows it to deform and return its shape in order to absorb concussional forces of movement.  There is enough deformation to diminish the force from the impact and load of the foot while preventing any damage to the internal structures of the foot and limb.  As load is placed on the foot, there is deformation that consists of:

• Expansion of the heels

• Sinking of the heels

• Inward movement of the dorsal wall

• Biaxial compression of the dorsal wall

• Depression of the coronary band

• Flattening of the sole

The hoof wall, bars and their association with the sole form the heel base with the purposes of providing traction, bearing the horse’s weight while allowing the stability and flexibility for the expansion of the hoof capsule that dissipates concussional forces on foot fall.  The sole is a highly keratinised structure like the hoof wall but made up of nearly 33% water so it is softer than the hoof wall and should be concave to allow the flattening of the sole on load application. The frog and heel bulbs serve a variety of special functions ranging from traction, protection, coordination, proprioception, shock absorption and the circulation of blood.  

When the foot lands on the ground, the elastic, blood-filled frog helps disperse some of the force away from the bones and joints, thus, acting as a shock absorber.  The venous plexus above the frog is involved in pumping blood from the foot back to the heart when the foot is loaded.  In addition, there is shielding of the deep digital flexor tendon and the sensitive digital cushion (soft tissue beneath the sole that separates the frog and the heel bulb from the underlying tendons and bones).  Like the heel bulbs, the frog has many sensory nerve endings allowing the horse to be aware of where his body and feet are and allows the horse to alter landing according to the condition of the ground (proprioception and coordination).  

The soft tissue structures comprise and form the palmar/plantar aspect of the foot.  The digital cushion lies between the lateral cartilages and above the frog and bars of the horse’s hoof.  This structure is composed of collagen, fibrocartilage, adipose tissue and elastic fibre bundles.  The digital cushion plays a role in shock absorption when the foot is loaded as well as a blood pumping mechanism.  Interestingly, it has been found that the digital cushion composition varies across and within breeds.  It is thought the variation of the composition of the digital cushion is partially dictated by a genetic predisposition.  In addition, the composition of the digital cushion changes with age.  As the horse ages the composition alters from elastic, fat and isolated collagen bundles to a stronger fibrocartilage.  Finally, the digital cushion and connective tissue within the foot have the ability to adapt to various external stimuli such as ground contact or body weight.   The lateral cartilage is a flexible sheet of fibrocartilage that suspends the pedal bone as well as acting as a spring to store and release energy. The lamina is a highly critical structure for hoof health.  The lamina lies between the hoof wall and the coffin bone.  There are two types of lamina known as the sensitive (dermal) lamina and insensitive (epidermal) lamina.  The insensitive lamina coming in from the hoof wall connects to the sensitive lamina layer that is attached to the coffin bone and these two types of lamina interdigitate with each other to form a bond.

Hoof and Musculoskeletal System

The hoof and the musculoskeletal system are closely linked and this is particularly observed in the posture of the horse when resting or moving.  Hoof shape and size and whether they are balanced directly affects the posture of the horse.  Ultimately, this posture will also affect the loads placed on the skeletal system, which affects bone remodelling. With an imbalance, bone pathologies of the limbs, spine and pelvis may occur such as osteoarthritis.  In addition, foot imbalances result in postural changes that lead to stress to the soft tissue structures that may lead to muscle injuries and/or tendon/ligament injuries.  

Conformation and hoof balance 

The terms balance and conformation are used frequently and used to describe the shape and size of the limb as a whole as well as the individual components of the limb and the spatial relations between them.  Balance is the term often used to describe the foot and can be viewed as a subset of conformation.  

Conformation should be considered when describing the static relations within the limb and excludes the foot.  Balance should be considered when describing the dynamic and static relationship between the horse’s foot and the ground and limb as well as within the hoof itself.  

These distinctions between conformation and balance are important to assess lameness and performance of the horse.  Additionally, this allows the veterinarian and farrier to find optimal balance for any given conformation.

The term hoof balance does lack an intrinsic definition.  The use of certain principles in order to define hoof balance, which in turn can be extended to have consistent evaluation of hoof balance as well as guide the trimming and shoeing regimens for each individual horse.  In addition, these principles can be used to improve hoof capsule distortion, modify hoof conformation and alter landing patterns of the foot.  These principles are:

• Evaluate hoof-pastern axis

• Evaluate centre of articulation

• The need for the heels to extend to the base of the frog

Assessing the horse’s foot balance by observing both static (geometric) balance and dynamic balance is vital.   Static balance is the balance of the foot as it sits on a level, clean, hard surface.  Dynamic balance is assessing the foot balance as the foot is in motion.  However, horses normally do not resemble the textbook examples of perfect conformation, which creates challenges for the farriers and veterinary surgeons.  The veterinarian should instigate further evaluation of the foot balance and any other ailments, in order to provide information that can be used by the farrier and veterinarian in formulating a strategy to help with the horse’s foot balance. With the farrier and veterinarian working cooperatively, the assessment of the hoof balance and shoeing of the foot should deliver a harmonious relationship between the horse’s limb, the hoof and the shoe.  

Dynamic Balance

The horse should be assessed in motion as one can observe the foot landing and placement.  A balanced foot when in motion should land symmetrically and flat when moving on a flat surface.  When viewed from the side, the heels and toe should land concurrently (flat foot landing) or even a slight heel first landing.  It is undesirable to have the toe landing first and often suggests pain localised to the heel region of the foot.  When observing the horse from the front and behind, both heel bulbs should land at the same time.  Sometimes, horses will land first slightly on the outside or lateral heel bulb of the foot but rarely will a horse land normally on the medial (inside) of the foot.  If the horse has no conformational abnormalities or pathologies the static balance will achieve the dynamic balance.  

Static Balance 

Hoof –pastern axis (HPA)

The hoof pastern axis (HPA) is a helpful guideline in assessing foot balance. With the horse standing square on a hard, level surface, a line drawn through the pastern and hoof should be parallel to the dorsal hoof wall and should be straight (unbroken).  The heel and toe angle should be within 5 degrees of each other. An underrun heel has been defined as the angle of the heel being 5 degrees less than the toe angle. The heel wall length should be roughly 1/3 of the dorsal wall.  In addition, the cannon (metacarpus/metatarsus) bone is perpendicular to the ground and when observed from the lateral side, the HPA should be a straight line.  When assessing the foot from the side, the dorsal hoof wall should be aligned with the pastern.  The optimal angle of the dorsal hoof wall is often cited as being 50-54°.  The length of the dorsal hoof wall is variable but guidelines have been suggested according to the weight of the horse. 

It is not uncommon that the hind feet are more upright compared to the fore feet at approximately 5 degrees.  A broken hoof-pastern axis is the most common hoof imbalance.  There are two presentations of a broken HPA known as a broken-back HPA and a broken-forward HPA.  These changes in HPA are often associated with two common hoof capsule distortions that include low or underrun heels and the upright or clubfoot, respectively.    

A broken-back hoof-pastern axis occurs when the angle of the dorsal hoof wall is lower than the angle of the dorsal pastern.  This presentation is commonly caused by low or underrun heel foot conformation accompanied with a long toe.  This foot imbalance is common and often thought to be normal with one study finding it present in 52% of the horse population.  With a low hoof angle, there is an extension of the coffin and pastern joints resulting in a delayed breakover and the heels bearing more of the horse's weight, which ultimately leads to excess stress in the deep digital flexor tendon as well as the structures around the navicular region including the bone itself.  

This leads to caudal foot pain so the horse lands toe first causing subsolar bruising.  In addition, this foot imbalance can contribute to chronic heel pain (bruising), quarter and heel cracks, coffin joint inflammation and caudal foot pain (navicular syndrome).   The cause of underrun heels is multifactorial with a possibility of a genetic predisposition where they may have or may acquire the same foot conformation as the parents.  There are also environmental factors such as excessive dryness or moisture that may lead to the imbalance.

A broken-forward hoof-pastern axis occurs at a high hoof angle with the angle of the dorsal hoof wall being higher than the dorsal pastern angle.  One can distinguish between a broken-forward HPA and a clubfoot with the use of radiographs.  With this foot imbalance, the heels grow long, which causes the bypassing of the soft tissue structures in the palmar/plantar area of the foot and leads to greater concussional forces on the bone.  This foot imbalance promotes the landing of the toe first and leads to coffin joint flexion as well as increases heel pressure.  The resulting pathologies that may occur are solar bruising, increased strain of the suspensory ligaments near the navicular bone and coffin joint inflammation.

Center of articulation

When the limb is viewed laterally, the centre of articulation is determined with a vertical line drawn from the centre of the lateral condyle of the short pastern to the ground.  This line should bisect the middle of the foot at the widest part of the foot and demonstrates the centre of articulation of the coffin joint.  The widest part of the foot (colloquially known as “Ducketts Bridge”) is the one point on the sole that remains constant despite the shape and size of the foot.  The distance and force on either side of the line drawn through the widest part of the foot should be equal, which provides biomechanical efficiency.    

Heels extending to the base of the frog

With respect to hoof balance, another component of the foot to assess is that the heels of the hoof capsule extend to the base of the frog.  The hoof capsule consists of the pedal bone occupying two-thirds of the space and one-third of the space is soft tissue structures. This area is involved in dissipating the concussional and loading forces and in order to ensure biomechanical efficiency both the bone and soft-tissue structures need to be enclosed in the hoof capsule in the same plane. 

To achieve this goal the hoof wall at the heels must extend to the base of the frog.  If the heels are allowed to migrate toward the centre of the foot or left too long then the function of the soft tissue structures have been transferred to the bones, which is undesirable.  If there is a limited amount to trim in the heels or a small amount of soft tissue mass is present in the palmar foot then some form of farriery is needed to extend the base of the frog (such as an extension of the branch of a shoe).    

Medio-lateral or latero-medial balance 

The medio-lateral balance is assessed by viewing the foot from the front and behind as well as from above with the foot raised.   To determine if the foot has medio-lateral balance, the hoof should be bisected or a line is drawn down the middle of the pastern down to the point of the toe.  

You should be able to visualise the same amount of hoof on both the left and right of that midline.  In addition, one should observe the same angle to the side of the hoof wall.  It is important to pick up the foot and look at the bottom.  Draw a line from the middle quarter (widest part of foot) on one side to the other then draw a line from the middle of the toe to the middle sulcus of the frog.  

This provides four quadrants with all quadrants being relatively the same in size (Proportions between 40/60 to 60/40 have been described as acceptable for the barefoot and are dependent on the hoof slope).  The frog width should be 50-60% of its length with a wide and shallow central sulcus.  The frog should be thick enough to be a part of the bearing surface of the foot.  The bars should be straight and not fold to the mid frog.  The sole should be concave and the intersection point of both lines should be the area of optimal biomechanical efficiency.  

The less concavity means the bone is nearer to the ground, thus, bearing greater concussional force.  Finally, assess the lateral and medial heel length.  Look down at the heel to determine the balance in the length of both heel bulbs.  Each heel bulb should be the same size and height.  If there are any irregularities with the heel bulbs then sheared heels may result, which is a painful condition.  Medio-lateral foot imbalance results in the uneven loading of the foot that leads to an accumulation of damage to the structures of the foot ultimately causing inflammation, pain, injury and lameness.   Soles vary in thickness but a uniform sole depth of 15mm is believed to be the minimum necessary for protection.  

Dorso-palmar/plantar (front to back – DP) balance

Refers to the overall hoof angle and the alignment of the hoof angle with the pastern angle when the cannon bone is perpendicular to the ground surface.  When assessing the foot from the side, the dorsal hoof wall should be aligned with the pastern.  The optimal angle of the dorsal hoof wall is often cited as being 50-54°.  The length of the dorsal hoof wall is variable but guidelines have been suggested according to the weight of the horse. 

The heel and toe angle should be within 5 degrees of each other. An underrun heel has been defined as the angle of the heel being 5 degrees less than the toe angle. The heel wall length should be roughly 1/3 of the dorsal wall.  

A line dropped from the first third of the coronet should bisect the base.  A vertical line that bisects the 3rd metacarpal bone should intersect the ground at the palmar aspect of the heels.

Radiographs

A useful way to assess trimming and foot balance is by having foot x-rays performed.  Radiography is the only thorough and conclusive method that allows one to determine if the foot is not balanced and the bony column (HPA) is aligned. 

Shoes should be removed and the foot cleaned before radiographs are executed.  The horse is often placed on foot blocks to elevate the feet off the ground so that the foot can be centred in the cassette and x-ray beam.  

Latero-medial view – The side view of the foot allows one to assess the dorsal and palmar aspects of the pedal bone as well as the navicular bone.  The horse should be standing squarely on a flat, level surface.  This projection is useful in determining the point of breakover and the hoof pastern axis should be parallel with the hoof wall.  The lateral view will demonstrate the length of the toe and the alignment of the dorsal surface of the pedal bone with the hoof wall, which should be parallel.  This view also allows one to determine the depth of the sole and inadequate solar depth is usually accompanied with excessive toe length (broken-back HPA). One may observe a clubfoot, broken forward.  

One can distinguish between a clubfoot and a broken-forward HPA with radiographs.  The broken-forward HPA the hoof angle of the heel is greater than the angle of the dorsal hoof wall.  The clubfoot also demonstrates these steep/high hoof angles but additionally the alignment of the coffin, short and long pastern bones are broken forward.

Dorsopalmar/plantar views - this “front to back” view is also performed with the horse standing squarely on 2 positioning blocks.  This projection allows the evaluation of medial to lateral balance and conformation of the foot with observation and measurement of the medial and lateral wall length and angle.  Horses with satisfactory conformation present with a parallel joint surface of the pedal bone to the ground.  The coffin joint should be even across its width.  In addition, the lateral and medial coronet and the lateral and medial walls are of equal thickness and the distance from the lateral and medial solar margins to the ground are similar. 

With foot imbalance, this author has observed that fore feet may have a higher lateral hoof wall, whereas, the hind feet may have a higher medial hoof wall.  It is worth noting that the pelvis, stifle and hocks are adapted to move laterally allowing a slight rotating action as it moves.  This action may cause uneven wear or poor trimming and shoeing may cause this limb movement to be out of line.  

Trimming

Often, trimming and shoeing are based on empirical experience that includes theoretical assumptions and aesthetic decisions.   The goals of trimming and shoeing are to facilitate breakover, ensure solar protection and provide heel support.  Trimming is the most important aspect of farriery because it creates the base to which a shoe is fitted.  Hoof conformation takes into account the function and shape of the foot in relation to the ground and lower limb both at rest and exercise.  Each individual foot should have a conformation that provides protection and strength while maximising biomechanical efficiency often viewed as foot balance. 

An important question that initially needs to be addressed is whether the horse requires shoes or not.  The answer does depend on what type of work the horse performs, what is the amount of workload, the conformation of the horse (especially the limbs and foot) and are there any previous or current injuries.  It must be stressed that the most important aspect, whether the horse is shod or not, is that the trim ensures an appropriately balanced foot for the horse. If there is poor trimming then this may lead to uneven and increased workload on the limb leading to an increased strain of the hoof and soft tissues (i.e. ligaments, tendons) that increase the risk of injury and developing acute and chronic lameness. 

The foot can be evaluated, trimmed and/or shod in a consistent, reproducible manner that considers:

Hoof-pastern axis (HPA)

The centre of articulation

Heels extending to the base of the frog

Appropriate trimming and shoeing to ensure the base of the foot is under the lateral cartilage; therefore, maximising the use of the digital cushion, can help in creating a highly effective haemodynamic mechanism.  Shoeing must be done that allows full functionality of the foot so that load and concessional forces are dissipated effectively.  

To implement appropriate farriery, initially observe the horse standing square on a hard service to confirm that the HPA is parallel.  If The HPA is broken forward or backward then these balances should be part of the trimming plan.  To determine the location of the centre of rotation, palpate the dorsal and palmar aspect of the short pastern just above the coronary band and a line dropped vertically from the centre of that line should correlate with the widest part of the foot. 

Shoeing

When the shoe is placed on the horse, the horse is no longer standing on its feet but on the shoe; therefore, shoeing is an extension of the trim.  The shoe must complement  the trim and must have the same biomechanical landmarks to ensure good foot balance.  It is this author’s view that the shoe should be the lightest and simplest possible.  The shoe must be placed central to the widest part of the foot and the distance from the breakover point to the widest part of the foot should be equal to the distance between the widest part of the foot and the heel. 

It has been shown that the use of shoes that lift the sole, frog and bars can reduce the efficient workings of the caudal foot and may lead to the prevalence of weak feet.  A study by Roepstorff demonstrated there was a reduced expansion and contraction of the shod foot but improved functionality of solar and frog support.   With this information, appropriate shoeing should allow increased functionality of the digital cushion, frog and bars of the foot, which improves the morphology and health of the hoof and reduces the risk of exceeding the hoof elasticity.  

Disease associated with hoof imbalance

Foot imbalance can lead to multiple ailments and pathologies in the horse.  It must be noted that the pathologies that may result are not necessarily exclusive for the foot but may expand to other components to the horse’s musculoskeletal system.  In addition, not one but multiple pathologies may result.  Diseases that may result from hoof imbalance are:

Conclusion

Foot balance is essential for your horse to lead a healthy and sound life and career. With a strong understanding of the horse anatomy and how foot imbalance can lead to lameness as well as other musculoskeletal ailments, one can work to assess and alter foot balance in order to ensure optimal performance and wellbeing of the horse.  It is essential that there is a team approach involving all stakeholders as well as the veterinarian and farrier in order to achieve foot balance. With focus on foot balance, one can make a good horse into a great horse.

Stem Cell Therapy - the improved diagnostics available to treat lameness

Article by Jackie Zions (interviewing Dr. Koenig)

Prevention is the ideal when it comes to lameness, but practically everyone who has owned horses has dealt with a lay-up due to an unforeseen injury at some point. The following article will provide tools to sharpen your eye for detecting lameness, review prevention tips and discuss the importance of early intervention. It will also begin with a glimpse into current research endeavouring to heal tendon injuries faster, which has obvious horse welfare benefits and supports horse owners eager to return to their training programs. Dr. Judith Koenig of Ontario Veterinary College (OVC) spends half of her time as a surgeon and teacher with a strong interest in equine sports medicine and rehabilitation, and the other half as a researcher at the OVC.

Lameness is a huge focus for Koenig, whose main interest is in tissue healing. “I think over the past 20 or 30 years we have become very, very good at diagnosing the cause of lameness,” says Koenig. “In the past, we had only radiographs and ultrasound as a diagnostic tool, but by now most referral centres also have MRI available; and that allows us to diagnose joint disease or tendon disease even more. We are much better now [at] finding causes that previously may have been missed with ultrasound.” 
Improvements in diagnostics have resulted in increased ability to target treatment plans. With all the different biologics on the market today, Koenig sees a shift in the management of joint disease with more people getting away from steroids as a treatment.

The following list is excerpted from Equine Guelph’s short course on lameness offered on TheHorsePortal.ca. It outlines the different diagnostics available:

When asked for the latest news on research she has been involved in, Koenig proclaims, “I'm most excited about the fact that horses are responding well to stem cell treatment—better than I have seen any response to any other drug we have tried so far!”

Koenig has investigated the use of many different modalities to see if they accelerate tissue healing and has studied which cellular pathways are affected. Two recent collaborative studies have produced very exciting findings, revealing future promise for treating equine osteoarthritis with stem cell therapy.  

In a safety study, Koenig and her team at the Ontario Veterinary College have shown equine pooled cryopreserved umbilical cord blood, (eCB) MSC, to be safe and effective in treatment of osteoarthritis.  

“These cells are the ones harvested from umbilical cord blood at the time of foaling and then that blood is taken to the lab and the stem cells are isolated out of it,” explains Koenig. The stem cells are then put through a variety of tests to make sure they are free of infectious diseases. Once given a clean bill of health, they are expanded and frozen. 
The stem cells harvested from multiple donors of equine umbilical cord blood [eCB, (kindly provided by eQcell), MSC] were compared to saline injections in research horses. “This type of cells is much more practical if you have a cell bank,” says Koenig. “You can treat more horses with it, and it’s off the shelf.” There were no systemic reactions in the safety study. Research has also shown no different reactions from sourcing from one donor or multiple donors.  

In the second study, 10 million stem cells per vial were frozen for use in healing OA from fetlock chips in horses that were previously conditioned to be fit. After the fetlock chip was created, exercise commenced for six more weeks, and then osteoarthritis was evaluated by MRI for a baseline. Half the horses were treated with the pooled MSC stem cells, and the control group received saline before another month of exercise. Then MRI and lameness exams were repeated, and arthroscopy was repeated to score the cartilage and remove the chip.

Lameness was decreased and cartilage scores were improved in the group that received stem cell therapy at the time of the second look with arthroscopy.

Many diagnostics were utilised during this study. MRIs, X-rays, ultrasounds and weekly lameness evaluations all revealed signs of osteoarthritis in fetlock joints improved in the group treated with (eCB) MSCs. After six weeks of treatment, the arthroscopic score was significantly lower (better cartilage) in the MSC group compared to the control group. 

“Using the MRI, we can also see a difference that the horses treated with stem cells had less progression of osteoarthritis, which I think is awesome,” says Koenig. “They were less lame when exercised after the stem cell therapy than the horses that received saline.”

This research group also just completed a clinical trial in client-owned horses diagnosed with fetlock injuries with mild to moderate osteoarthritis changes. The horses were given either 10 million or 20 million stem cells and rechecked three weeks and six weeks after the treatment. Upon re-evaluation, the grade of lameness improved in all the horses by at least one. Only two horses presented a mild transient reaction, which dissipated after 48 hours without any need for antibiotics. The horse’s joints looked normal, with any filling in the joint reduced.
There was no difference in the 18 horses, with nine given 10 million stem cells and the other nine 20 million stem cells; so in the next clinical trial, 10 million stem cells will be used.

The research team is very happy with the results of this first-of-its-kind trial, proving that umbilical cord blood stem cells stopped the progression of osteoarthritis and that the cartilage looked better in the horses that received treatment. The future of stem cell therapy is quite promising!
Rehabilitation
Research has shown adhering to a veterinary-prescribed rehabilitation protocol results in a far better outcome than paddock turn out alone. It is beneficial for tendon healing to have a certain amount of controlled stimulation. “These horses have a much better outcome than the horses that are treated with just being turned out in a paddock for half a year,” emphasises Koenig. “They do much better if they follow an exercise program. Of course, it is important not to overdo it.”

For example, Koenig cautions against skipping hand-walking if it has been advised.  It can be so integral to stimulating healing, as proven in recent clinical trials. “The people that followed the rehab instructions together with the stem cell treatment in our last study—those horses all returned to racing,” said Koenig.  

“It is super important to follow the rehab instructions when it comes to how long to rest and not to start back too early.”

Another concern when rehabilitating an injured horse would be administering any home remedies that you haven't discussed with your veterinarian. Examples included blistering an area that is actively healing or applying  shockwave to mask pain and then commence exercise.

Prevention and Training Tips
While stating there are many methods and opinions when it comes to training horses, Koenig offered a few common subjects backed by research. The first being the importance of daily turnout for young developing horses.  

Turnout and exercise
Many studies have looked at the quality of cartilage in young horses with ample access to turn out versus those without. It has been determined that young horses that lack exercise and are kept in a stall have very poor quality cartilage.
Horses that are started early with light exercise (like trotting short distances and a bit of hill work) and that have access to daily paddock turnout, had much better quality of cartilage. Koenig cited research from Dr. Pieter Brama and similar research groups.

Another study shows that muscle and tendon development depend greatly on low grade exercise in young horses.  Evaluations at 18 months of age found that the group that had paddock turnout and a little bit of exercise such as running up and down hills had better quality cartilage, tendon and muscle.  

Koenig provides a human comparison, with the example of people that recover quicker from injury when they have been active as teenagers and undergone some beneficial conditioning. The inference can be made that horses developing cardiovascular fitness at a young age stand to benefit their whole lives from the early muscle development.

Koenig says it takes six weeks to regain muscle strength after injury, but anywhere from four to six months for bone to develop strength. It needs to be repeatedly loaded, but one should not do anything too crazy! Gradual introduction of exercise is the rule of thumb.

Rest and Recovery
“Ideally they have two rest days a week, but one rest day a week as a minimum,” says Koenig. “I cannot stress enough the importance of periods of rest after strenuous work, and if you notice any type of filling in the joints after workout, you should definitely rest the horse for a couple of days and apply ice to any structures that are filled or tendons or muscles that are hard.” 

Not purporting to be a trainer, Koenig does state that two speed workouts a week would be a maximum to allow for proper recovery. You will also want to make sure they have enough access to salt/electrolytes and water after training.

During a post-Covid interview, Koenig imparted important advice for bringing horses back into work methodically when they have experienced significant time off.
“You need to allow at least a six-week training period for the athletes to be slowly brought back and build up muscle mass and cardiovascular fitness,” says Koenig.  “Both stamina and muscle mass need to be retrained.”

Watch video: “Lameness research - What precautions do you take to start training after time off?” https://www.youtube.com/watch?v=zNHba_nXi2k

The importance was stressed to check the horse’s legs for heat and swelling before and after every ride and to always pick out the feet. A good period of walking is required in the warmup and cool down; and riders need to pay attention to soundness in the walk before commencing their work out.

Footing and Cross Training
With a European background, Koenig is no stranger to the varying track surfaces used in their training programs. Statistics suggest fewer injuries with horses that are running on turf. 

Working on hard track surfaces has been known to increase the chance of injury, but delving into footing is beyond the scope of this article.

“Cross training is very important,” says Koenig. “It is critical for the mental and proper musculoskeletal development of the athlete to have for every three training days a day off, or even better provide cross-training like trail riding on these days." 

Cross-training can mitigate overtraining, giving the body and mind a mental break from intense training. It can increase motivation and also musculoskeletal strength. Varied loading from training on different terrain at different gaits means bone and muscle will be loaded differently, therefore reducing repetitive strain that can cause lameness.

Hoof care
Whether it is a horse coming back from injury, or a young horse beginning training, a proficient farrier is indispensable to ensure proper balance when trimming the feet. In fact, balancing the hoof right from the start is paramount because if they have some conformational abnormalities, like abnormal angles, they tend to load one side of their joint or bone more than the other. This predisposes them to potentially losing bone elasticity on the side they load more because the bone will lay down more calcium on that side, trying to make it stronger; but it actually makes the bone plate under the cartilage brittle.  

Koenig could not overstate the importance of excellent hoof care when it comes to joint health and advises strongly to invest in a good blacksmith. Many conformational issues can be averted by having a skilled farrier right from the time they are foals. Of course, it would be remiss not to mention that prevention truly begins with nutrition. “It starts with how the broodmare is fed to prevent development of orthopaedic disease,” says Koenig. Consulting with an equine nutritionist certainly plays a role in healthy bone development and keeping horses sound.

Lower limb anatomy and how it can be conditioned for racing

Article by Adam Jackson MRCVS 

Better understanding the appropriate levels of exercise and training while the horse’s body grows and develops has been a topic of research for many years. Although it has been shown that young, growing horses are well-suited to adapt to conditioning, it is vital that continued research is performed in order to develop thoughtful and strategic training methods to promote healthy, fit and sound horses with long careers and lives.  

Horses’ limbs consist of dozens of muscles, bones, tendons, ligaments, and joints that allow the horse to move as well as support its body weight. The limbs function to provide thrust and movement while absorbing impact and bearing weight.  Most of the horse’s weight is supported by the fore limbs, while the propulsion of the horse is provided by the hind limbs. In addition, the horse has two apparatuses referred to as the stay apparatus and suspensory apparatus. The stay apparatus allows major joints in the limbs to lock so that the horse may rest and relax while standing. The suspensory apparatus is designed to absorb shock, carry the horse’s weight, and prevent the overextension of joints. Finally, the hooves are important structures that maintain support and traction as well as provide additional shock absorption.  

Since the cardiovascular system provides blood supply throughout the body, by responding to various stimuli, it can control the velocity and amount of blood carried through the vessels, thus, delivering oxygen, nutrients, hormones, and other important substances to cells and organs in the body.  It plays a very important role in meeting the body’s demands during exercise, stress, and activity.  

Exercise is used to increase the body’s ability to withstand repeated bouts of similar exercise with less impact.  With a strong and healthy cardiovascular system, there is an improved ability of the musculoskeletal system receiving oxygen, thus, allowing muscles to better their capacity to use oxygen and energy.  However, the adaptation period for each of these physiological systems do differ as the cardiovascular system adapts faster compared to the musculoskeletal system. This is often an overlooked consideration when developing training programmes for horses. 

It is important to understand the various functions, structures, and adaptive processes of the horse’s musculoskeletal system such as bone, articular cartilage, tendons, and ligaments in order to develop appropriate training regimens. 

Bone has many important roles that involve locomotion, the storage of minerals (especially calcium and phosphate), soft tissue and vital organ protection, and the support and containment of bone marrow. Bone is a specialised connective tissue, and together with cartilage forms the strong and rigid endoskeleton.  The bone is continuously altering through two processes called bone modelling and bone remodelling, involving four cells referred to as osteoclasts, osteoblasts, osteocytes and bone lining cells.  

Osteoblasts secrete bone matrix in the form of non-mineralised osteoid, which is then mineralised over a few weeks to form a bone matrix.  Osteoclasts are involved in resorption of bone as this process occurs faster than the formation of bone. When the bone surfaces are not in the development or resorption phase, the bone surface is completely lined by a layer of flattened and elongated cells termed bone-lining cells.  Osteocytes are derived from osteoblasts and are highly specialised to maintain the bone matrix.  They are designed to survive hypoxic conditions and maintain biomineralisation of the bone matrix.  Osteocytes also control osteoblastic and osteoclastic activities allowing bone remodelling.

The function of bone modelling is to alter and maintain shape during growth. As the horse grows and develops, bone modelling occurs with the acquisition and removal of bone.  While the young horse grows and develops, bone modelling allows the bone to endure strains from everyday work and exercise. The adult skeleton undergoes a minimal amount of bone modelling. Due to the presence of the high frequency of bone modelling in young horses, their skeletal strength is highly influenced by strains to their bones during exercise and daily use. With this knowledge, it has been concluded and confirmed that short-term dynamic exercise of an adolescent can lead to beneficial changes to its bone morphology.  

Bone remodelling is a different process, in which old and damaged bone is renewed, which enables the bone to respond and adapt to changing functional situations. Bone remodelling is usually a coordinated relationship between bone resorption and bone formation. This process occurs throughout the horse’s life with the renewal of primary, damaged or old bone. Osteoclasts absorb old and damaged bone, and the osteoblasts form new bone and lay down new bone matrix until the earlier absorbed bone is replaced. In those animals with musculoskeletal disease or damage, there is an imbalance of osteoblast and osteoclast activity. With the knowledge that osteoblast activity to make new bone takes months whilst osteoclast activity of removing old and damaged bone only takes a few days to two weeks, bone that is being repaired is at a high risk of further injury as bone removed has not been completely replaced.   Multiple studies have shown that exercise while growing can provide lifelong benefits; however, it must be done with care and knowledge.

In addition, many studies have shown that exercise of a dynamic nature in moderate distances, such as that achieved in the pasture or prescribed short-distance high-speed work is beneficial to musculoskeletal development and may prevent injuries when entering race training. It has also been observed that long slow work does not increase bone strength. Below is a summary of the young horse response of the various types of exercise.

Articular cartilage is a highly specialised connective tissue found in joints with the role of providing a smooth, lubricated surface of articulation and to help transmit loads with a low amount of friction. The articular cartilage is a hyaline cartilage (flexible and strong tissue providing a smooth, slippery surface) with a dense “ExtraCellular Matrix” (ECM) consisting of specialised cells called chondrocytes, collagen and proteoglycans. These components help to retain water in the ECM that is required for the joints mechanical properties. As age increases, hydration of the matrix does decrease, resulting in stiffness. Chondrocytes are residential cells in articular cartilage that play a role in the development, maintenance, and repair of the ECM. They do respond to a variety of stimuli, including mechanical loads, growth factors, hydrostatic pressures, piezoelectric forces (formation of electric charge with force). Because of the lack of blood vessels, lymphatics, and nerves as well as being a harsh biomechanical environment, there is a limited capacity to heal and repair. In addition, chondrocytes have limited potential for replication, thus, have limited healing capacity; and chondrocytes survival depends on an optimal chemical and mechanical environment.  

Maintaining joint health is vital, which requires the preservation of healthy cartilage tissue. Inactivity of joints is detrimental to articular cartilage; thus, regular movement of joints and dynamic loads is needed to provide a normal articular cartilage structure and function. Biochemical responses of the cartilage to exercise are not nearly as well known compared to bone. While the confinement of young horses stunts joint development, excessive straining of cartilage can also reduce joint development. It has been observed that pasture access was optimal for the development of joints and the confinement or excessive sprint exercise (12–32 sprints of 40 metres for 6 days a week for 5 months) causes detrimental effects on the joint and may be deemed as unnatural exercise.  It is also thought that exercise is needed well before two years of age to allow cartilage thickening as well as the avoidance of confinement. It can be concluded that further studies are required with respect to level of exercise and type of exercise in order to achieve healthy cartilage tissue as there is clearly a fine line between frequency and intensity of exercise.  

Tendons and ligaments are distinct but closely related tissues that have unique and important roles in musculoskeletal function and musculoskeletal disease. Tendons and ligaments are dense, fibrous connective tissues that connect muscle to bone or bone to bone, respectively.  These tissues transmit mechanical forces to stabilise the skeleton and allow body movement.  Tendons and ligaments consist mainly of collagen type I as well as small amounts of collagen III, IV, V, and VI. There are also various proteoglycans in tendons and ligaments that both organise and lubricate collagen fibre bundles. The elasticity of tendons and ligaments is due to the large amount of type I collagen. During locomotion, the tendon decreases energy cost to the horse by acting as a spring to store and release energy while stretching and recoiling in the stance and swing phases of each stride. Tendons and ligaments have blood vessels and nerves that allow the homeostasis and response to injury.  

Tenocytes are tightly regulated by a series of growth factors and transcription factors that allow the synthesis, maintenance, and the degradation of the tendon extracellular matrix. Tendons are elastic, but tearing may occur if there is excessive loading on the tendon and the repair of collagen is a slow process. In addition, tendons have crimp morphology where the tendons buckle in a state of relaxation and act as shock absorbers.  Unbuckling of the tendon occurs during loading.  This crimp morphology may be disturbed if an injury occurs and also is reduced in older horses.  

Due to the variation of activity of tenocytes in foals and young horses, it has been observed that both a lack of exercise and excess of exercise can impair tendon make-up and subsequent functionality. With the current data and research that has been gathered, it can be concluded that if horses take advantage of spontaneous exercise when in the paddocks (which they often do), the developing tendons may benefit and be at a lower risk of injury when racing training starts. 

Conclusion

It is clear that further research is needed in order to ascertain the optimal amount and type of exercise that is needed in order to provide a strong musculoskeletal system and functional performance. However, it has been shown that prescribed exercise during the growth of the horse can increase the longevity of the horse’s health and performance. It has been observed that confinement and the lack of loading can result in weaker tissues and the loss of function of none, tendons, ligaments and articular cartilage.  However, it must also be recognised that medical attempts to alleviate pain so that a horse can continue to train through an injury can greatly increase tissue damage which is detrimental to the horse’s health and career. It is far more beneficial to provide an adequate amount of time for the injury to heal, thus, putting the horse’s health and wellbeing as a top priority.  

Nutritional Perspective

Bone development in yearlings from the sales ring to racing

Article by Des Cronin B.Ag.Sc, MBA

Maintaining the equine skeleton is vital to ensure optimal development of the young growing horse, minimise risk of injury in the performance horse, and promote longevity and soundness.

The skeletal development and health of a young horse begins in utero and ensuring the broodmare receives the correct intake of key nutrients will be critical to the growth of the unborn foal. Producing high-quality milk places a significant drain on the mineral reserves of the mare. Maintaining mineral intakes during peak lactation is vital to ensure the foal receives the best nutrition to support the rapid skeletal development in the early weeks and months of growth. During this time, bone formation, body size, and muscle mass greatly increase. Risk of defective bone and related tissue formation increases with one of more of the following:

• Poor diet with the incorrect balance of energy and nutrients in the daily ration

• Inadequate amounts of calcium (Ca) and phosphorus (P)

• A reversed Ca:P ratio

• Low zinc (Zn) or copper (Cu) in the diet

• Low Vitamin D

Feeding a young horse for a maximum growth rate is undesirable because bone hardening lags greatly behind bone lengthening. At 12 months old, the young horse could reach about 90 to 95 per cent of its mature height but only about 75 per cent of its mature bone mineral content.

Ideally, young horses should gain weight at a rate that their developing bones can easily support. Growing bones and connective tissues don’t have the strength to support rapid weight gain from overfeeding, especially energy. Rapid weight gain can also make other skeletal anomalies worse. In these cases the risk of developmental orthopaedic disorders (DOD) and unsoundness increases.

DOD and unsoundness can also occur during uneven growth. For example, switching an underfed, slow-growing horse to a good diet that allows quick growth (compensatory growth), increases the risk of DOD. Foals between the ages of 3 and 9 months of age are at greatest risk of DOD.

Fresh forages, for example grazed grass, usually provide enough major minerals such as calcium (Ca) and phosphorus (P) for the growing horse. However, there can be significant variation in calcium and phosphorus levels in all forages but particularly preserved forages (hay and haylage). Forage analysis should always be undertaken to determine mineral composition. 

For young fast-growing horses, the diet must supply the quantities of calcium and phosphorus needed for normal bone formation. In terms of Ca:P ratio, the ratio must be positive in favour of calcium. Horses are much more tolerant of high-dietary calcium than other species. For practical purposes, a good guideline would be to keep the ratio Ca:P between 1.5 to 1 and 2.5 to 1.  Grains (e.g., oats) contain 10 per cent of the calcium level found in typical forages. Grains are poor sources of calcium, both in terms of the amount of calcium supplied and their effect on Ca:P ratio in the diet. Where grains are fed, supplementation will be necessary to balance the diet.  

While some forages may contain adequate calcium and phosphorus, they will typically supply less than 20 per cent of the daily requirements for trace elements. Supplementation of trace elements will generally be necessary to support normal bone development.

Where concentrates are fed (especially low levels), supplementation may still be necessary to balance the overall mineral and trace element intake. Nutritional advice should be sought to ensure the horse's diet is correctly balanced.

To meet the carefully balanced requirements of key minerals, it is advisable to supplement the daily rations of growing horses and young horses entering training with an appropriate nutritional product. 

Make sure that the supplement used contains the correct ratio of calcium and phosphorus, as well as other key nutrients such as vitamin D and chelated trace elements (copper, manganese, and zinc) to support normal bone development.

Supplementing branch chain amino acids in the diet ensures that growth is maintained. Lysine plays a key role when protein concentrations in the body are low. Vitamin A supports collagen formation, which is a key component of the supportive structures of joints (tendons and ligaments). Vitamin D3 is added to enhance calcium absorption.

Although growth rates slow after the age of two, they are still juvenile in their skeletal development with some growth plates, such as the shoulder and stifles, yet to completely close. Although they may look like fully grown adults, it is still important to meet nutritional requirements especially if starting training and work. With the addition of exercise and training, a young horse's nutritional needs change.  The added forces from groundwork on the long bones and increased requirements of other nutrients like electrolytes need to be considered. 

Finally, horses all grow and develop at different rates because of factors such as genetics. Some youngsters will need  more support for longer periods of time than others, so it is important to manage accordingly.

Air Quality and Air Pollution’s Impact on Your Horse’s Lungs

There’s nothing like hearing a horse cough to set people scurrying around the barn to identify the culprit. After all, that cough could mean choke, or a respiratory virus has found its way into the barn. It could also indicate equine asthma. Yes, even those “everyday coughs” that we sometimes dismiss as "summer cough" or "hay cough" are a wake-up call to the potential for severe equine asthma. 

Formerly known as heaves, broken wind, emphysema, chronic obstructive pulmonary disease (COPD), or recurrent airway obstruction (RAO), this respiratory condition is now called severe equine asthma (sEA). These names reflect how our scientific and medical understanding of this debilitating disease has changed over the years. We now consider heaves to be most comparable to severe asthma in people.

But what if your horse only coughs during or after exercise? This type of cough can mean that they have upper airway irritation (think throat and windpipe) or lower airway inflammation (think lungs) meaning inflammatory airway disease (IAD), which is now known as mild-to-moderate equine asthma (mEA). This airway disease is similar to childhood asthma, meaning  that it can go away on its own. However, it is still very important to call your veterinarian out to diagnose mEA. This disease causes reduced athletic performance, and there are different subtypes of mEA that benefit from specific medical therapies. In some cases, mEA progresses to sEA.

Equine Asthma and  Air Quality
What does equine asthma have to do with air quality? A lot, it turns out. Poor air quality, or air pollution, includes the barn dusts—the allergens and moulds in hay and the ground-up bacteria in manure, as well as arena dusts and ammonia from urine. Also, very importantly for both people and horses, air pollution can be from gas and diesel-powered equipment. This includes equipment being driven through the barn, the truck left idling by a stall window, or the smog from even a small city that drifts nearly invisibly over the surrounding farmland. Recently, forest-fire smoke has been another serious contributor to air pollution. 

Smog causes the lung inflammation associated with mEA. Therefore, it is also likely that air pollution from engines and forest fires will also trigger asthma attacks in horses with sEA. Smog and smoke contain many harmful particulates and gases, but very importantly they also contain fine particulate matter known as PM2.5. The 2.5 refers to the diameter of the particle being 2.5 microns. That’s roughly 30 times smaller than the diameter of a human hair. Because it is so small, this fine particulate is inhaled deeply into the lungs where it crosses over into the bloodstream. So, not only does PM2.5 cause lung disease, but it also causes inflammation elsewhere in the body including the heart. Worldwide, even short-term exposure is associated with an increased risk of premature death from heart disease, stroke, and lung cancer. This PM2.5 stuff is not trivial!

In horses, we know that PM2.5 causes mEA, so it’s logical that smog and forest-fire smoke exposure could exacerbate asthma in horses, but we don’t know about heart disease or risk of premature death.

Symptoms, Diagnostic Tests and Treatments

Equine asthma manifests with a spectrum of symptoms that vary in severity and the degree of debilitation they cause. Just like in people with asthma, the airways of horses with mEA and sEA are “hyperreactive.” This means that the asthmatic horse’s airways are extra sensitive to barn dusts that another horse’s lungs would just “ignore.” The asthmatic horse’s airways constrict, or become narrower, in response to these dusts. This narrowing makes it harder to get air in and out of the lungs. Think about drinking through a straw. You can drink faster with a wider straw than a skinnier one. It’s the same with air and the airways. In horses with mEA, the narrowing is mild. In horses with sEA, the constriction is extreme and is the reason why they develop the “heaves line”; they have to use their abdominal muscles to help squeeze their lungs to force the air back out of their narrow airways. They also develop flaring of their nostrils at rest to make their upper airway wider to get more air in. Horses with mEA do not develop a heaves line, but the airway narrowing and inflammation do cause reduced athletic ability.

The major signs of mEA are coughing during or just after exercise that has been going on for at least a month and decreased athletic performance. In some cases, there may also be white or watery nasal discharge particularly after exercise. Often, the signs of mEA are subtle and require a very astute owner, trainer, groom, or rider to recognise them.

Another very obvious feature of horses with sEA is their persistent hacking cough, which worsens in dusty conditions. “Hello dusty hay, arena, and track!” The cough develops because of airway hyperreactivity and because of inflammation and excess mucus in the airways. Mucus is the normal response of the lung to the presence of inhaled tiny particles or other irritants. Mucus traps these noxious substances so they can be coughed out, which protects the lung. But if an asthma-prone horse is constantly exposed to a dusty environment, it leads to chronic inflammation and mucus accumulation, and the development or worsening of asthma along with that characteristic cough.

Accurately Diagnosing Equine Asthma

Veterinarians use a combination of the information you tell them, their observation of the horse and the barn, and a careful physical and respiratory examination that often involves “rebreathing.” This is a technique where a bag is briefly placed over the horse’s nose, causing them to breathe more frequently and more deeply to make their lungs sound louder. This helps your veterinarian hear subtle changes in air movement through the lungs and amplifies the wheezes and crackles that characterise a horse experiencing a severe asthma attack. Wheezes indicate air “whistling” through constricted airways, and crackles mean airway fluid buildup. The fluid accumulation is caused by airway inflammation and contributes to the challenge of getting air into the lung. 

Other tests your veterinarian might use are endoscopy, bronchoalveolar lavage, and in the specialist setting, pulmonary function testing. They will also perform a complete blood count and biochemical profile assay to help rule out the presence of an infectious disease. 

Endoscopy allows your veterinarian to see the mucus in the trachea and large airways of the lung. It also lets them see whether there are physical changes to the shape of the airways, which can be seen in horses with sEA. 

Bronchoalveolar lavage, or “lung wash” is how your veterinarian assesses whether there is an accumulation of mucus and inflammatory cells in the smallest airways that are too deep in the lung to be seen using the endoscope. Examining lung wash fluid is a very important way to differentiate between the different types of mEA, between sEA in remission and an active asthma attack, and conditions like pneumonia or a viral lung infection. 

Finally, if your veterinarian is from a specialty practice or a veterinary teaching hospital, they might also perform pulmonary function testing. This allows your veterinarian to determine if your horse’s lungs have hyperreactive airways (the hallmark of asthma), lung stiffening, and a reduced ability to breathe properly. 

Results from these tests are crucial to understanding the severity and prognosis of the condition. As noted earlier, mEA can go away on its own; but medical intervention may speed healing and the return to athletic performance. With sEA, remission from an asthmatic flare is the best we can achieve.  As the disease gets worse over time, eventually the affected horse may need to be euthanised.

Management, Treatment and Most Importantly—Prevention
Successful treatment of mEA and sEA flares, as well as long-term management, requires a multi-pronged approach and strict adherence to your veterinarian’s recommendations.

Rest is important because forcing your horse to exercise when they are in an asthma attack further damages the lung and impedes healing.  To help avoid lung damage when smog or forest-fire smoke is high, a very useful tool is your local, online, air quality index (just search on the name of your closest city or town and “AQI”).  Available worldwide, the AQI gives advice on how much activity is appropriate for people with lung and heart conditions, which are easily applied to your horse. For example, if your horse has sEA and if the AQI guidelines say that asthmatic people should limit their activity, then do the same for your horse. If the AQI says that the air quality is bad enough that even healthy people should avoid physical activity, then do the same for you AND your horse. During times of poor air quality, it is recommended to monitor the AQI forecast and plan to bring horses into the barn when the AQI is high and to turn them out once the AQI has improved.

Prevent dusty air. Think of running your finger along your tack box – whatever comes away on your finger is what your horse is breathing in. Reducing dust is critical to preventing the development of mEA and sEA, and for managing the horse in an asthmatic flare. 

Logical daily practices to help reduce dust exposure:

• Turn out all horses before stall cleaning

• Wet down the aisle prior to sweeping

• Never sweep debris into your horse’s stall

• Use low-dust bedding like wood shavings or dust-extracted straw products, which should also be dampened down with water

• Reduce arena, paddock, and track dust with watering and maintenance

• Consider low-dust materials when selecting a footing substrate

• Steam (per the machine’s instructions) or soaking hay (15–30 minutes and then draining, but never store steamed or soaked hay!) 

• Feed hay from the ground

• Feed other low-dust feeds

• Avoid hay feeding systems that allow the horse to put their nose into the middle of dry hay—this creates a “nosebag” of dust

Other critical factors include ensuring that the temperature, humidity and ventilation of your barn are seasonally optimised. Horses prefer a temperature between 10–24 ºC (50–75 ºF), ideal barn humidity is between 60–70%. Optimal air exchange in summer is 142 L/s (300 cubic feet/minute). For those regions that experience winter, air exchange of 12–19 L/s (25–40 cubic feet/minute) is ideal. In winter, needing to strip down to a single layer to do chores implies that your barn is not adequately ventilated for your horse’s optimal health. Comfortable for people is often too hot and too musty for your horse! 

Medical interventions for controlling asthma are numerous. If your veterinarian chooses to perform a lung wash, they will tailor the drug therapy of your asthmatic horse to the results of the wash fluid examination. Most veterinarians will prescribe bronchodilators to alleviate airway constriction. They will also recommend aerosolised, nebulised or systemic drugs (usually a corticosteroid, an immunomodulatory drug like interferon-α, or a mast cell stabilisers like cromolyn sodium) to manage the underlying inflammation. They may also suggest nebulising with sterile saline to help loosen airway mucus and may suggest feed additives like omega 3 fatty acids, which may have beneficial effects on airway inflammation. 

New Research and Future Directions

Ongoing research is paramount to expanding our knowledge of what causes equine asthma and exploring innovative medical solutions. Scientists are actively investigating the effects of smog and barn dusts on the lungs of horses. They are also working to identify new targeted therapies, immunotherapies and other treatment modalities to improve outcomes for affected horses.

Conclusion

Both mild and severe equine asthma are caused and triggered by the same air pollutants, highlighting the need for careful barn management. The alarming rise in air pollution levels poses an additional threat to equine respiratory health. Recognising everyday coughs as potential warning signs and implementing proper diagnostic tests, day-to-day management practices and medical therapies are crucial in combating equine asthma. By prioritising the protection of our horse’s respiratory health and staying informed about the latest research, we can ensure the well-being of our equine companions for years to come.

Gastric ulcers in racehorses – what trainers should know

Article by Dr Michael Hewetson

Why are gastric ulcers so important in racehorses?

Gastric ulcers are very prevalent in racehorses, with between 52% and 93% of horses in active training affected. This is significant, because gastric ulcers can impact both the horse's performance and its overall health and welfare, which in turn can have financial and competitive implications for their owners, trainers, and the racing industry as a whole. 

Gastric ulcers can affect a horse's performance by causing abdominal discomfort and reduced appetite. This can lead to changes in stride length and decreased energy levels that may impact their racing performance. Horses with gastric ulcers may also exhibit changes in behaviour, such as nervousness, aggression, or reluctance to train or race, which again, can affect their overall performance and temperament. If left untreated, gastric ulcers can lead to more serious health concerns such as colic, potentially requiring costly medical intervention and downtime for the horse. But most importantly, gastric ulcers are a welfare issue for the Thoroughbred racing industry, and with growing public scrutiny on the industry, ensuring the well-being of racehorses is a priority, and addressing gastric ulcers promptly should be considered part of responsible horse management. This requires a close working relationship with your vet, who will be able to give you expert advice about diagnosis, treatment, and management of this frustrating disease. 

Understanding gastric ulcers

FIGURE 1

Equine gastric ulcer syndrome (EGUS) is a general term used to describe erosions and ulcers of the horse’s stomach and is similar to the term peptic ulcer disease in people. Unlike people however, the horse is unique in that the stomach lining (mucosa) is divided into an upper squamous and a lower glandular portion (figure 1); and it is important to realise that there are differences between these two regions with respect to how these lesions develop, their prevalence, associated risk factors and response to treatment. Therefore, when referring to EGUS, your vet may use the terms Equine Squamous Gastric Disease (ESGD) and Equine Glandular Gastric Disease (EGGD) to clearly distinguish the anatomical region of the stomach affected. 

FIGURE 2

There does not appear to be a clear relationship between the presence of squamous disease and glandular disease, and the fact that both conditions may occur concurrently in the same horse does not indicate that they are associated. In the case of squamous disease, the cause of the ulcers is well understood, with a variety of managemental risk factors (e.g. increase in exercise intensity, low roughage/high starch diet, stall confinement) contributing to an increase in the exposure of the squamous mucosa to acid. The squamous mucosa is not normally exposed to acid. As such it is inherently susceptible to acid injury, and with prolonged acid exposure, ulcers may develop (figure 2).

FIGURE 3

In contrast to squamous disease, the cause of glandular disease is poorly understood. The glandular mucosa is fundamentally different from the squamous mucosa in that it is exposed to a highly acidic environment under normal physiological conditions. As such, it is only when there is a breakdown of the normal defence mechanisms that protect the glandular mucosa from acidic gastric contents that glandular disease occurs. While ulcers are most commonly seen with squamous disease, horses with glandular disease rarely present with ulcers. Rather, the lesions are more consistent with an erosive inflammatory gastritis and can vary widely in their appearance (figure 3). There is a now evidence to suggest that stress, both psychological (e.g. multiple riders or caretakers; confinement; stress associated with transport and competition) and physiological (e.g. increases in the total amount and frequency of exercise without adequate rest periods) may increase the risk of glandular disease in horses. This may be due to a variety of mechanisms including a reduction in the mucus coating and blood supply to the glandular mucosa; both of which compromise the gastric barrier, resulting in acid injury.

The prevalence of gastric ulcers appears to vary with age, use, stage of training, as well as the region of the stomach affected. The prevalence of squamous disease is consistently highest in performance horses, with 52-93% of Thoroughbred racehorses found to be affected. The prevalence of glandular disease is less well reported, however up to 47% of Thoroughbred racehorses may be affected. 

Why are racehorses so susceptible to gastric ulcers?

It is most likely because of their unique management when compared to most other horse populations; and the intensity of exercise that is inherent of racing competition. For example, it has been shown that the risk of squamous disease increases with an increase in the intensity of exercise and the duration of time at work. Strenuous exercise causes an increase in intra abdominal pressure associated with contraction of the abdominal muscles1. This results in compression of the stomach, and exposure of the sensitive squamous mucosa to acidic gastric content (acid splash). Strenuous exercise has also been shown to cause an increase in a hormone called gastrin, which stimulates acid production in the stomach. 

Several factors associated with management have also been shown to increase the risk of squamous disease, many of which are imposed on racehorses at the commencement of training or during racing competition. These include a high starch/low roughage diet, intermittent fasting, stall confinement, transport, intermittent access to water and administration of hypertonic solutions of electrolytes. In fact, exposure to a combination of a high starch diet, stall confinement and strenuous exercise has been shown to induce ulcers in as little as 7 days; and intermittent fasting is so effective at inducing ulcers that it is used as a model for squamous disease in experimental studies. Thoroughbred racehorses are also exposed to many of the risk factors for glandular disease, most notably, multiple riders or caretakers; confinement; and stress associated with transport and competition.

How do you know if your horse has gastric ulcers and how might they affect performance?

A variety of clinical signs may suggest that a horse has gastric ulcers, however there is currently very little evidence to support a direct association between any of these signs and the presence or absence of ulcers seen on gastroscopy. This is likely because most of the clinical signs are non-specific and are often very subjective. This is complicated further by the fact that horses with gastric ulcers may not demonstrate clinical signs and if they do, the signs do not necessarily correlate with the severity of the lesions seen on gastroscopy. Clinical signs suggestive of gastric ulcers should therefore always be interpreted with caution, and most importantly, gastroscopy should always be performed to confirm the disease (figure 4).

In racehorses, gastric ulcers have been associated with poor appetite, poor body condition, changes in behaviour (including an aggressive or nervous attitude), post prandial colic, stereotypic behaviour and resentment of girthing. Any one of these clinical signs can potentially have an indirect effect on performance (for example, through reduced appetite or interruption in training), but the big question is if gastric ulcers themselves, in the absence of other clinical signs, have an effect on performance. Despite the fact that it is a well entrenched ’fact’ amongst trainers that gastric ulcers have a direct effect on poor performance or reluctance to train, there is surprisingly little evidence in the literature to back this up. This may be in part due to the difficulties in excluding the many confounding factors that might influence poor performance (e.g. lameness, respiratory disease etc.). 

The mechanism by which gastric ulcers may affect performance has not been identified but is likely to be related to epigastric pain. In people, epigastric pain is defined as pain localised to an area below the sternum and above the umbilicus and is common in athletes with gastro-oesophageal reflux disease (GERD). Acid reflux onto the sensitive squamous mucosa of the oesophagus during exercise causes a “burning sensation” that gets worse with increasing exercise intensity and has been shown to affect performance. Horses with squamous gastric disease have similar lesions to those causing GERD in human athletes, and the problem is likely to be exacerbated by the fact that the squamous mucosa extends from the oesophagus into the upper one-third of the stomach and is not protected by an oesophageal sphincter. Interestingly, a recent study in human athletes suggested that GERD may be associated with increased abdominal pressure during exercise, a mechanism that I have already alluded to in the equine athlete. How exactly epigastric pain impacts on athletic performance in the horse is a matter of ongoing speculation. One theory is that it may affect stride length. It has been shown that horses with gastric ulcers have a reduced stride length when galloping, likely due to abdominal discomfort. Stride length and lung ventilation are mechanically coupled in the galloping horse, and therefore, reduced stride length will result in decreased oxygen uptake, thus limiting aerobic capacity during peak exercise.

How are gastric ulcers treated and what can you do to prevent them?

Let’s turn our attention now to the treatment of gastric ulcers. Because there is currently little evidence to suggest an association between clinical signs and the presence or severity of gastric ulcers, treatment should always be based on gastroscopic evidence of ulcers. Some trainers may still choose to commence treatment based entirely on clinic signs without gastroscopy and assess for a clinical response. I would caution against this approach, as it can be costly if the horse does not have ulcers, and gastroscopy is still going to be necessary to conclusively rule out gastric ulcers if clinical improvement is not seen with treatment.

Treatment of gastric ulcers will vary depending upon the severity and the location of the ulcers and your vet will be able to give you advice on the best approach. In most cases treatment consists of management and dietary modification in conjunction with the use of proton pump inhibitors which suppress acid production. Oral omeprazole is the drug of choice and is currently the only licensed drug for the treatment and prevention of gastric ulcers in horses in the UK and Ireland.   

Administering oral omeprazole on an empty stomach can improve the bioavailability of the drug. This can be achieved practically by administering it first thing in the morning at least 1 hour prior to feeding. This ensures the stomach will be empty as horses eat very little during the night even if they have access to forage. 

The duration of treatment will depend on the location of the lesions, with squamous disease tending to heal faster than glandular disease. In most cases, your vet will prescribe oral omeprazole for 3-4 weeks and then the requirement for additional medication will be determined following a repeat gastroscopy. In the case of glandular disease, oral omeprazole is often combined with sucralfate, which adheres to the damaged mucosa, providing a physical barrier while also stimulating mucus secretion, both of which reduce potential exposure to acid. Omeprazole is a controlled drug, and therefore needs to be withdrawn prior to competition. The BHA published detection time for oral omeprazole is ≤ 48hrs, so withdrawal of the drug 3-5 days before competition would be prudent. There is, however, some concern that the requirement for withdrawal times might influence the efficacy of oral omeprazole treatment in racehorses. Many vets report reoccurrence of squamous disease following discontinuation of treatment with omeprazole, often within as little as 3 days, and this was demonstrated in a recent study comparing withholding periods for oral omeprazole treatments in racing Thoroughbreds6. The authors reported a squamous disease prevalence of 83% in horses after a “2 clear days'' recommended withholding period for oral omeprazole, which was an increase from 25% of horses with squamous disease before the recommended withholding period, and they theorised that ‘rebound acid secretion’ may be implicated. This phenomenon occurs following the discontinuation of proton pump inhibitor drugs such as oral omeprazole, and is linked to a loss of negative feedback from gastric acid during treatment that causes an increased secretion of the hormone gastrin that can persist for up to 2-4 days after the last dose of omeprazole has been administered. This results in a short period of increased gastric acid production when treatment is stopped. Whilst nothing can currently be done about the required withdrawal periods during racing, strict management practices should be implemented for the 2-4 days following cessation of omeprazole treatment to mitigate against development of squamous gastric disease. This could include ensuring provision of adequate roughage during this time, avoiding fasting or withholding water, and perhaps limiting exercise or transport if possible.

Additional management and dietary adaptations which may help prevent gastric ulcers and can be implemented longer term in a racing yard include free choice access to roughage (and if not, ensuring that roughage is provided at intervals of no more than 4-6 hours); turn out into a paddock with good quality grazing where possible; a low starch/high fat diet (or alternatively, smaller concentrate meals more frequently); reduction/avoidance of any potential stressors; and provision of regular rest days. Where possible, training schedules should be adjusted so that they occur later in the day when enough roughage has been consumed to ensure that there is a mat of roughage in the stomach to buffer acid in the upper squamous portion and to reduce acid splash during exercise. Alternatively, a handful of palatable chaff should be fed 20 minutes prior to exercise. 

Numerous supplements are marketed for prevention of gastric ulcers, however there is currently very limited evidence to support their use.

References

1. Lorenzo-Figueras M, Merritt AM. Effects of exercise on gastric volume and pH in the proximal portion of the stomach of horses. Am J Vet Res. 2002;63(11):1481–1487. 

2. Vatistas NJ, Sifferman RL, Holste J, et al. Induction and maintenance of gastric ulceration in horses in simulated race training. Equine Vet J Suppl. 1999;29:40–44. 

3. Murray MJ, Eichorn ES. Effects of intermittent feed deprivation, intermittent feed deprivation with ranitidine administration, and stall confinement with ad libitum access to hay on gastric ulceration in horses. Am J Vet Res. 1996;57(11):1599–1603.

4. Herregods TV, van Hoeij FB, Oors JM, Bredenoord AJ, Smout AJ. Effect of running on gastroesophageal reflux and reflux mechanisms. Am J Gastroenterol. 2016;111(7):940–946. doi:10.1038/ajg.2016.122

5. Nieto JE, Snyder JR, Vatistas NJ, Jones JH. Effect of gastric ulceration on physiologic responses to exercise in horses. Am J Vet Res. 2009;70(6):787–795. 

6. Shan R, Steel CM, Sykes B. The Impact of Two Recommended Withholding Periods for Omeprazole and the Use of a Nutraceutical Supplement on Recurrence of Equine Gastric Ulcer Syndrome in Thoroughbred Racehorses. Animals. 2023; 13(11):1823. 

7. Clark B, Steel C, Vokes J, Shan JR, Gedye K, Lovett A, Sykes BW. Evaluation of the effects of medium-term (57-day) omeprazole administration and of omeprazole discontinuation on serum gastrin and serum chromogranin A concentrations in the horse. J Vet Intern Med. 2023 Jul-Aug;37(4):1537-1543.

The Gerald Leigh Memorial Lectures 2023

The Gerald Leigh Memorial Lectures, is an annual  gathering devoted to the racing industry and the health and wellbeing of the horses involved.  

This year, equine veterinarians, researchers, students and industry professionals from around the world attended the event, held June 8, 2023, at the historic Tattersalls Sales in Newmarket, England.  

There were insightful and informative lectures that educated the attendants but also instigated a healthy, lively debate on the health and welfare of the training and competing of horses. The underlying theme that was present during the whole event was all members of the conference had a deep passion and commitment to continuously progress and improve on managing the welfare and wellbeing of the horses in the industry, both on and off of the track.  

Two very special guest speakers, Sir Mark Prescott and Luca Cumani, wonderfully illustrated these sentiments as they described their reflections on the improvement and enhancement of horse safety.  

Horse racing may be regarded as an elite sport, and all activities involving horses have an element of risk. All stakeholders in the racing industry must continuously work to ensure that the risks are minimised in order to reduce the number of injuries and fatalities that may occur in training and on the racecourse.  There are now well-publicised concerns regarding the acceptability of exposing horses to risk in racing.  These lectures and all of the attendees embraced the values of the public will so that there can be continued acceptance of horse sports.   

Reducing the incidence of fractures in racing 

Christopher Riggs of The Hong Kong Jockey Club clearly outlined the various strategies to reduce the risk of fractures in racehorses. There are two principal strategies that may used to reduce the incidence of severe fractures in horses while racing and training:

1. Identifying extrinsic factors that increase risk and take action to minimise them. 

An example would be investigating different racing surfaces in order to determine which may provide the safest racing surface. However, studies have provided limited evidence and support for subtle extrinsic factors.

2. Identifying individuals that are at increased risk and prevent them from racing or minimise that risk until the risk has subsided.  

There are many research routes that are being undertaken to identify those horses that may be at a higher risk of fractures. There are investigations involving heritability and molecular studies that may provide evidence of genetic predisposition to fracture. However, Dr. Riggs explained that further understanding of the relationship between genetic, epigenetic and environmental factors is required before genetic screening is likely to be of practical use.  

Pre-race screening of horses by diligent clinical examination is poor at reducing the incidence of fracture. Dr. Riggs described another strategy that may assist with a clinical examination that is the use of biomarkers in blood and urine.  

Unfortunately, the precision to be of practical value has so far remained relatively unrewarding.  Wearable technology that records biometric parameters, including stride characteristics, has shown some promise in identifying horses that are at increased risk of fracture; although Dr. Riggs explained that this work requires further development.  

Finally, Dr. Riggs described both the use and current limitations of  diagnostic imaging in identifying pre-fracture pathology in order to identify a horse at imminent risk of fracture.  He conceded that further knowledge of the significance of the range of abnormalities that can be detected by imaging is incomplete.

Dr. Riggs concluded his lecture by expressing that the implementation of  diagnostic imaging to screen  “high-risk” horses identified through genetic, epidemiology, biomarkers and/or biometrics may be the best hope to reduce the incidence of racing fractures. This field can be advanced with further studies, especially of a longitudinal nature.

Professor Tim Parkin of Bristol Veterinary School discussed the need for further investment in welfare research and education. One avenue of investment that should be seriously considered is the analysis of data related to (fatal) injuries in Thoroughbred racing over the last 25 years.  

It was expressed, with the abundance of data that has been collected, that some risk factors would be relatively simple to identify. An encouraging example in the collection and use of data to develop models in predicting and potentially preventing injury has been conducted by the Hong Kong Jockey Club funded by the Hong Kong Jockey Club Equine Welfare Research Foundation. This may provide an opportunity to pilot the use of risk profiling to contribute to decision-making about race entries.  In addition, the results of the pilot study combined with other sources of data may encourage race authorities to mandate the collection of veterinary and training data in order to help in risk mitigation.

Horse racing is an international sport, and there are different governing bodies that ensure racing integrity. However, the concept of social licence equestrian sports and Thoroughbred horse racing continues to gain significant public attention.  Therefore, racing governing bodies are increasingly aiming to provide societal assurances on equine welfare. 

Dr. Ramzan of Rossdales Veterinary Surgeons provided an eloquent and clear message during his lecture that race yard veterinarians and trainers are instrumental in ensuring good horse health and welfare and reducing serious injury of the horse both while training or racing, which will provide sufficient trust and legitimacy from the public and society.  This feasible goal can be reached with good awareness of members involved in the care and training of each individual horse and conveying this information and any concerns to their veterinarian.  The veterinarian can also contribute by honing their knowledge and skills and working closely with yard staff in order to make appropriate and better targeted veterinary intervention.   

In the last two decades, there has been an incredible evolution and exciting developments in diagnostic imaging in the veterinary profession. It is believed that these technologies can provide a significant contribution to helping in mitigating fracture risks to racehorses on the course and in training.  

Professor Mathieu Spriet of University of California, Davis, described how these improvements in diagnostic imaging has led to the detection of early lesions as well as allowing the monitoring of the lesions’ evolution.  

He continued by explaining the strengths and limitations of different imaging modalities such as computed tomography (CT), magnetic resonance imaging (MRI) and positron emission tomography (PET).  Being one of the leaders in the use of PET in equine veterinary medicine, he presented further insight on how this particular modality provides high-resolution 3-D bone scans while being very sensitive to the identification of bone turn-over prior to the development of structural changes and allowing one to distinguish between active and inactive processes when structural changes are present.  

He concluded his impressive lecture by providing evidence with amazing PET images that the role of imaging is not merely for diagnostic purposes to characterise clinical abnormalities, but can also be used as a screening tool in certain horse populations for fracture risk assessment or for the monitoring of lesions to provide clearance for racing. 

Fractures, due to bone overloading rather than direct trauma occur commonly in Thoroughbred racehorses and are the leading cause of euthanasia on the racecourse. Despite many changes to race conditions, the number of catastrophic fractures has remained relatively static, with approximately 60 horses a year having a fatal fracture during a race in the UK.  

Against this backdrop, there have been great developments in the diagnosis and treatment of fractures in the last 40 years. Prevention of racecourse and training fractures would be ideal so the development of efficacious techniques to screen horses at risk may reduce the incidence and preserve social licensing.  

One technique discussed by Dr. Ian Wright of Newmarket Equine Referrals was to help mitigate the impact of racecourse fractures, which would be acute immobilisation of racecourse fractures, thus, reducing associated pain and anxiety while optimising clinical outcome and reducing on course fatality rates. Because of our increased understanding of fracture pathogenesis and their associated biomechanics, effective fracture immobilisation has been made possible. The majority of fractures that occur in flat racing and between obstacles in jump racing, are a result of stress or fatigue failure of the bone and not associated with trauma.  

In addition, fractures seen on the racecourse are often found in the same specific sites (i.e., metacarpal/metatarsal condyles and the proximal sesamoid bones of the fetlock) and have repeatable configurations. With this understanding and knowledge, racecourse veterinarians can optimally immobilise a fracture in a logical and pre-planned manner.  

As Dr. Wright expressed, this allows the fracture patient to have reduced pain and anxiety and enable the horse to be moved from the course comfortably so that it can be further examined. Ultimately, this allows the veterinarian and all stakeholders to make effective and judicious decisions for the sake of the horse’s welfare and wellbeing. As Dr. Wright concluded, this benefits both horses and racing.

Dr. Debbie Guest of the Royal Veterinary College discussed a different approach in mitigating the risk of fractures during training and racing by developing novel tools to reduce catastrophic fractures Thoroughbreds. Because it has been found that some horses are more inherently predisposed to fractures than other horses, Dr. Guest and her team have developed a genome-wide polygenic risk score so that one can potentially calculate an individual horse’s risk of fracturing during training or racing compared to the population as a whole.  

This strategy may contribute in identifying genetically high-risk horses so that additional monitoring of the patients can be exercised during their careers and also leading to fracture risk, which are found to be the cause of approximately half of these incidents.  

The system of using DNA testing to identify biological processes that may or may not be present ultimately leading to fracture risk may be a powerful tool in lowering the risk of catastrophic fracture and requires further research and application.

Cardiac events & sudden cardiac death in training and racing

In racehorses, sudden death that is associated with exercise on the racetrack or during training is a serious risk to jockeys and adversely affects horse welfare and the public perception of the sport. It is believed 75% of race day fatalities result from euthanasia following a catastrophic injury. The other 25% of fatalities is due to sudden deaths and cardiac arrhythmias are found to be the cause of approximately half of these incidents. The lectures focused on this area of concern by providing three interesting lectures on cardiac issues in the racehorse industry.  

Dr. Laura Nath of the University of Adelaide, explained the difficulties in identifying horses that are at risk of sudden cardiac death. It is believed that part of the solution to this difficult issue is the further development and use of wearable devices including ECG and heart rate monitors.  

With the use of these technologies, the goal would be to recognise those horses that are not progressing appropriately through their training and screen these horses for further evaluation. This course of action has been seen in human athletes that develop irregular rhythms that are known to cause sudden cardiac death with the use of computational ECG analysis, even when the ECGs appear normal on initial visual inspection.  

Knowing that ECGs and particularly P-waves are used as a non-invasive electrocardiographic marker for atrial remodelling in humans, Dr. Nath recently completed a study on the analysis variations in the P-wave seen on ECGs in athletic horses and found that increases of P-waves in racehorses are associated with structural and electrical remodelling in the heart and may increase the risk of atrial fibrillation (cardiac event).

Dr. Celia Marr of Rossdales Veterinary Surgeons continued the discussion of cardiac disease in both the training and racing of horses. Unfortunately, cardiac disease knowledge does lag compared to musculoskeletal and respiratory diseases when considering the causes of poor performance in racehorses. Due to the fact that cardiac rhythm disturbances are fairly common, occurring in around 5–10% of training sessions in healthy horses in Newmarket and over 50% of horses investigated for poor performance, Dr. Marr expressed the need for further research and investigation in this area.  

In addition, this research needs to determine if there is indeed a link between heart rhythm disturbances and repeated episodes of poor performance and sudden cardiac arrest. ECGs and associated technologies are helpful, but there are limitations such as the fact that rhythm disturbances do not always occur every time the horse is exercised.  Therefore, it would be of great value that a robust criterion is established when evaluating ECGs in racehorses. The Horserace Betting Levy Board has provided funding for investigation by initially exploring the natural history of paroxysmal atrial fibrillation (self-correcting form) to understand risk factors and predict outcomes for affected horses.

Continuing the theme of the lectures on irregular heart rhythms and associated sudden cardiac death (SCD) in training and racing, Professor Kamalan Jeevaratnam described his exciting research in using artificial intelligence (AI) to identify horses at increased risk of developing irregular rhythms that may cause SCD.  

AI is an exciting and rapidly expanding field of computer science that is beginning to be implemented in veterinary medicine. With funding by the Horserace Betting Levy Board and the Grayson Jockey Club Research Foundation, Professor Jeevaratnam of the University of Surrey, has piloted three novel algorithms that help predict horses with rhythm abnormalities through the analysis of horses’ ECGs.  

It was acknowledged that further research is required to develop this technology by using data collected from multiple sources, but the initial results are promising in the development of an useful AI tool to identify horses at risk of SCD and prevent catastrophic events, thus, ensuring the welfare of the horse in racing.

Conclusion

The Gerald Leigh Memorial Lectures was a thoroughly successful and enjoyable event attended by a variety of different members of the horse racing industry. Not only did the lecturers provide interesting and valuable information but also excitement for the future of racing.  It was very clear that all the lecturers and attendees were passionate and committed to the racehorse welfare and wellbeing as well as retaining the social licence for an exciting sport. 

Thermoregulation in horses

Article by Adam Jackson - MRCVS

Exertional heat illness (EHI) is a complex disease where thoroughbred racehorses are at significant risk due to the fact that their workload is intensive in combination with the high rate of heat production associated with its metabolism.  In order to understand how this disease manifests and to develop preventative measures and treatments, it is important to understand thermoregulation in horses. 

What is thermoregulation?

With continuous alteration in the surrounding temperature, thermoregulation allows the horse to maintain its body temperature within certain limits.  Thermoregulation is part of the greater process of homeostasis, which is a number of self-regulating processes the horse uses to maintain body stability in the face of changing external conditions.  Homeostasis and thermoregulation are vital for the horse to maintain its internal environment to ensure its health while disruption of these processes leads to diseases. 

The horse’s normal temperature range is 37.5–38.5°C (99–101°F).  Hyperthermia is the condition in which the body temperature increases above normal due to heat increasing faster than the body can reduce it. Hypothermia is the opposite condition, where the body temperature decreases below normal levels as the body is losing heat faster than producing it.   These conditions are due to the malfunction of thermoregulatory and homeostatic control mechanisms.

Horses are colloquially referred to as warm-blooded mammals—also known as endotherms because they maintain and regulate their core body, and this is opposite ectotherms such as reptiles.  The exercising horse converts stored chemical energy into mechanical energy when contracting various muscles in its body. However, this process is relatively inefficient because it loses roughly 80% of energy released from energy stores as heat. The horse must have effective ways to dissipate this generated heat; otherwise, the raised body temperatures may be life threatening.

Transfer of body heat

There are multiple ways heat may be transferred, and this will flow from one area to another by:

1. Evaporation 

The main way body heat is lost during warm temperatures is through the process of evaporation of water from the horse’s body surface. It is a combination of perspiration, sweating and panting that allows evaporation to occur.

Sweating is an inefficient process because the evaporation rate may exceed the body heat produced by the horse, resulting in the horse becoming covered and dripping sweat. This phenomenon occurs faster with humid weather (high pressure).

Insensible perspiration is the loss of water through the skin, which does not occur as perceivable sweat. Insensible perspiration takes place at an almost constant rate and is the evaporative loss from skin; but unlike sweating, the fluid loss is pure water with no solutes (salts) lost. The horse uses insensible perspiration to cool its body.

It is not common for horses to pant in order to dissipate heat; however, there is evidence that the respiratory tract of the horse can aid in evaporative heat loss through panting.

2. Conduction

Conduction is the process where heat is transferred from a hot object to a colder object, and in the case of the horse, this heat transfer is between its body and the air.  However, the air has poor thermal conductivity, meaning that conduction plays a small role in thermoregulation of the horse.   Conduction may help if the horse is lying in a cool area or is bathed in cool water.  

The horse has the greatest temperature changes occurring at its extremities, such as its distal limbs and head.  The horse can alter its blood flow by constricting or dilating its blood vessels in order to prevent heat loss or overheating, respectively. 

Interestingly, the horse will lie down and draw its limbs close to its body in order to reduce its surface area and to control conduction. There also have been some adaptive changes in other equids like mules and burros, where shorter limbs, longer ears and leaner bodies increase its surface area to help in heat loss tolerance.

3. Convection 

Convection is the rising motion of warmer areas of a liquid or gas and the sinking motion of cooler areas of the liquid or gas.  Convection is continuously taking place between the surface of the body and the surrounding air. Free convection at the skin surface causes heat loss if the temperature is low with additional forced convective heat transfer with wind blowing across the body surface.

When faced with cold weather, a thick hair coat insulates and resists heat transfer because it traps air close to the skin; thus, preventing heat loss. Whereas, the horse has a fine hair coat in the summer to help in heat loss.

4. Radiation

Radiation is the movement of heat between objects without direct physical contact.  Solar radiation is received from the sun and can be significant in hot environments, especially if the horse is exposed for long periods of time.  A horse standing in bright sunlight can absorb a large amount of solar radiation that can exceed its metabolic heat production, which may cause heat stress. 

How the horse regulates its body temperature

The horse must regulate its heat production and heat loss using thermoregulatory mechanisms.  There are many peripheral thermoreceptors that detect changes in temperature, which leads to the production of proportional nerve impulses. These thermoregulators are located in the skin skeletal muscles, the abdomen, the spinal cord and the midbrain with the hypothalamus being instrumental in regulating the internal temperature of the horse.   A coordinating centre in the central nervous system receives these nerve incoming impulses and produces output signals to organs that will alter the body temperature by acting to reduce heat loss or eliminate accumulated heat.  

The racehorse and thermoregulation

The main source of body heat accumulation in the racehorse is associated with muscular contraction.  At the initiation of exercise, the racehorse’s metabolic heat production, arising from muscle contraction, increases abruptly.  The heat production does alter the level of intensity of the work as well as the type of exercise undertaken.  

During exercise, the core body temperature increases because heat is generated and the horse’s blood system distributes this heat throughout the body. Hodgson and colleagues have theorised and confirmed via treadmill studies that the racehorse has the highest rate of heat production compared to other sporting horses. In fact, the racehorse’s body temperature can rise 0.8°C per minute, reaching 42.0°C. But what core temperature can the horse tolerate and not succumb to heat illness and mortality?  The critical temperature for EHI (exertional heat illness) is not known, but studies have demonstrated that a racehorse can be found to have core temperatures between 42–43°C without any clinical symptoms. Currently, anecdotal evidence is only available, suggesting that a core temperature of 43.5°C will result in manifestation of EHI with the horse demonstrating central nervous system dysfunction such as ataxia (incoordination).  In addition, temperatures greater than 44°C result in collapse. 

Heat loss in horses

A horse loses heat to the environment by a combination of convection, evaporation and radiation, which is magnified during racing due to airflow across the body. However, if body heat gained through racing is not minimised by convection, then the racehorse’s body temperature is regulated entirely by evaporation of sweat. This evaporation takes place on the horse’s skin surface and respiratory tract.  

The horse has highly effective sweat glands found in both haired and hairless skin, which produces sweat rates that are highest in the animal kingdom.   Efficient evaporative cooling is present in the horse because its sweat has a protein called latherin, which acts as a wetting agent (surfactant); this allows the sweat to move from its skin to the hair.

Because of the horse’s highly blood-rich mucosa of its upper respiratory tract, the horse has a very efficient and effective heat exchange system.  Estimates suggest this pathway dissipates 30% of generated heat by the horse during exercise.  As the horse exercises, there is blood vessel dilation, which increases blood flow to the mucosa that allows more heat to be dissipated to the environment. When the respiratory tract maximises evaporative heat loss, the horse begins to pant. Panting is a respiratory rate greater than 120 breaths per minute with the presence of dilated nostrils; and the horse adopts a rocking motion. However, if humidity is high, the ability to evaporate heat via the respiratory route and skin surface is impaired. The respiratory evaporative heat loss allows the cooling of venous blood that drains from the face and scalp. This blood may be up to 3.0°C cooler than the core body temperature of 42.0°C. And as it enters the central circulatory system, it can significantly have a whole-body cooling effect. This system is likely an underestimated and significant means to cool the horse.

Pathophysiology of EHI  in the thoroughbred

Although it is inconsistent to determine what temperature may lead to exertional heat illness (EHI), it is known that strenuous exercise, especially during heat stress conditions leads to this disease.  In human medicine, this disease is recognised when nervous system dysfunction becomes apparent.  There are two suggested pathways that lead to EHI, which may work independently or in combination depending on the environmental factors that are present during racing/training.

1. Heat toxicity pathway

Heat is known to detrimentally affect cells by denaturing proteins leading to irreversible damage.  In general, heat causes damage to cells of the vascular system leading to widespread intravascular coagulation (blood clot formation), pathologically observed as micro thrombi (miniature blood clots) deposits in the kidneys, heart, lungs and liver.  Ultimately, this leads to damaged organs and their failure.

Heat tissue damage depends on the degree of heat as well as the exposure time to this heat. Mammalian tissue has a level of thermal damage at 240 minutes at 42°C, 60 minutes at 43°C, 30 minutes at 44°C or 15 minutes at 45°C.  This heat damage must be borne in mind following a race requiring suitable and appropriate cooling methods, otherwise inadequate cooling may lead to extended periods of thermal damage causing disease. 

The traditional viewpoint is that EHI is caused by strenuous exercise in extreme heat and/or humidity.  However, recent studies have revealed that environmental conditions may only cause 43% of EHI cases, thus, suggesting that other factors are involved.

2. Heat sepsis pathway

In some instances. a horse suffering from EHI may present with symptoms and clinical signs similar to sepsis like that seen in an acute bacterial infection. 

A bacterial infection leading to sepsis causes an extreme body response and a life threatening medical emergency.  Sepsis triggers a chain reaction throughout the body particularly affecting the lungs, urinary tract, skin and gastrointestinal tract.

Strenuous exercise in combination with adverse environmental conditions may lead to sepsis without the presence of a bacterial infection— also known as an endotoxemic pathway—causing poor oxygen supply to the mucosal gastrointestinal barrier. Ultimately, the integrity of the gastrointestinal tract is compromised, allowing endotoxins to enter the blood system and resulting in exercise-induced gastrointestinal syndrome (EIGS).

However, researchers have observed that EHI in racehorses is unpredictable as EHI may develop in horses following exercise despite “safe” environmental conditions.  Even with adequate cooling and resuscitative therapies, tissue damage that occurs demonstrates that thermoregulatory and inflammatory pathways may vary, and hyperthermia may be the trigger but may not necessarily be driving the condition.

Diagnosis of EHI

The diagnosis of EHI is based on the malfunctioning of the central nervous system.

Initially, hyperthermia reduces the blood flow to the cerebrum of the brain, leading to a decrease of oxygen to that area—also known as ischemia. As a result, the clinical signs are:

• Extreme restlessness

• Confusion

• Substantial headache

If this hyperthermia continues, then the blood-brain barrier (an immunological barrier between circulating blood that may contain microorganisms like bacteria and viruses to the central nervous system) begins to leak plasma proteins, resulting in cerebral oedema (build up of fluid causing affected organ to become swollen). If treatment is not initiated at this point, then neuronal injury will result especially in the cerebellum.

EHI follows and involves serious CNS dysfunction.  The clinical signs associated with EHI are:

• Delirium

• Horses unaware of their surroundings

The final stage of EHI occurs when the swollen oedematous brain compresses vital tissue causing cellular damage. The clinical signs of end-stage EHI are:

• Collapse

• Unconsciousness

• Coma

• Death

Definition of EHI

EHI most commonly occurs immediately after a race when the horse is panting, sweating profusely and may be dripping with sweat. The most reliable indication of EHI is clinical signs associated with the dysfunction of the central nervous system in the presence of hyperthermia. Researchers have provided descriptions of levels of CNS dysfunction, ranging from level 1 to level 4.

Level 1 – The earliest recognizable signs of CNS dysfunction

The horse becomes restless, agitated and irritable. There is often head nodding or head shaking. The horse is difficult to restrain and will not stand still.  Therapeutic intervention such as cooling can resolve these clinical signs, but if the horse is inadequately cooled then the disease can escalate. 

Level 2 – Obvious neurological dysfunction

Often misdiagnosed as colic symptoms, the horse becomes further agitated and irritable with the horse kicking out without any particular stimulus present. This stage is dangerous to all handlers involved as the horse’s behaviour is unpredictable. 

Level 3 – Bizarre neurological signs

At this stage, the horse has an altered mentation appearing vacant, glassy-eyed and “spaced-out”.  In addition, there is extreme disorientation with a head tilt and leaning to one side with varying levels of ataxia (wobbly).  It has been observed that horses may walk forward, stop, rear and throw themselves backwards.  It is a very dangerous stage, as horses are known to run at fences, obstacles and people. Horses may also present as having a hind limb lameness appearing as a fractured leg with hopping on the good limb.  These clinical signs may resolve with treatment intervention.

Level 4 – Severe CNS dysfunction

There is severe CNS dysfunction at this stage of EHI with extreme ataxia, disorientation and lack of unawareness of its surroundings. The horse will continuously stagger and repeatedly fall down and get up while possibly colliding with people or objects with a plunging action. Unsurprising, the horse is at risk of severe and significant injury.  Eventual collapse with the loss of consciousness and even death may arise.

Treatment of EHI

In order to achieve success in the treatment of EHI, it is imperative that there is early detection, rapid assessment and aggressive cooling. The shorter the period is between recognising the condition and treatment, the greater the chance of a successful outcome.  In particular settings such as racecourses or on particularly hot and humid days, events must be properly equipped with easily accessible veterinary care and cooling devices. It is highly effective if a trained worker inspects every horse in order to identify those horses at risk or exhibiting symptoms. 

If EHI is recognised, veterinary intervention will be paramount in the recovery to prevent further illness and suppress symptoms. It will be important to note any withdrawal periods of any non-steroidal anti-inflammatories (NSAIDs) and analgesics before returning to racing. There are a number of effective ways to cool the horse with easily accessible resources.

Whole body cooling systems

Cooling the horse with ice-cold water is an effective way to draw heat from the underlying tissues. In addition, cooling the skin redistributes cooled blood back to the central circulatory system thus reducing thermal strain with the cooling of core body temperature.

The system that works best for horses due to its size is spray cooling heat transfer. It is ideal to have two operators to spray either side of the horse. It is recommended to begin at the head and neck followed by the chest and forelimbs then the body, hind limbs and between the legs. Spray nozzles are recommended to provide an even coverage of the skin surface.   

Dousing is another technique in which horses are placed in stalls and showered continuously until the condition resolves. Pouring buckets over the entire body of the horse is not recommended as most of the water falls to the ground, thus, not efficient at cooling the horse. 

Because most horses suffer from EHI immediately after the race, the appropriate location for inspection, cooling systems and veterinary care should be in the dismounting yard and tie-up stalls.  There must be an adequate supply of ice to ensure ice-cold water treatment. 

When treating a horse with EHI, there must be continuous and uninterrupted cooling until the CNS dysfunction has disappeared. 
When the skin surface temperature decreases to 30°C, cutaneous skin vessels begin to disappear; CNS function returns to normal, and there is the normalisation of behaviour. Cooling can be stopped, and the horse can be walked once CNS abnormalities have resolved. It must remain closely monitored for a further 30 minutes in a well-ventilated and shaded region. It is important that they are not unattended.

Scraping sweat off of the horse must only be done if the conditions are humid with no airflow.  However, if it is hot and there is good airflow, scraping is unnecessary because the sweat will evaporate.

Cooling collars

During strenuous exercise, there is a combination of heat production in the brain, reduced cerebral blood flow, creating cerebral ischaemia as well as the brain being perfused with hot blood. It is believed that cooling the carotid artery that aids in blood perfusion of the brain might be a strategy to cool the brain. A large collar is placed on either side and around the full length of the horse’s neck and is cooled by crushed ice providing a heat sink around the carotid artery; and it is able to pump cooled blood into the brain. 

Another possible benefit of this device is the cooling of the jugular veins, which lie adjacent to the carotid arteries.  The cooled blood in the jugular veins enter the heart and is pumped to the rest of the body, hence, potentially cooling the whole body. In addition, it is thought that the cooling of the carotid artery causes it to dilate, allowing greater blood flow into the brain. 

Provision of shaded areas

Shaded areas with surfaces that reflect heat, dry fans providing air flow and strategically placed hoses to provide cool water is an important welfare initiative at racecourses in order to minimise risk of EHI and treat when necessary. 

Conclusion

The most effective treatment of EHI is the early detection of the disease as well as post-race infrastructure that allows monitoring of horses in cooling conditions, while providing easily accessible treatment modalities when they are needed.  

Evaluating the horse’s central nervous system dysfunction is essential to recognise both the disease as well as monitoring the progression of the disease. CNS dysfunction allows one to define the severity of the condition. 

Understanding the pathophysiology of EHI is essential. It is important to recognise that it is a complex condition where both the inflammatory and thermoregulatory pathways work in combination. With a better understanding of these pathways, more effective treatment for this disease may be found.