Trust your gut - the importance of feeding the gut microbiome for health, performance & longevity

Article by Dr. Richard McCormick, M.V.B., Dip. Eq.Sc., M.R.C.V.S. 

The science of equine nutrition is really quite simple – The horse is a flight animal and in the wild, needs to be able to escape from predators using a short burst of energy. Nutrition and subsequent ‘energy’ for survival is all provided by grass which has the required balance of vitamins, minerals, immune supportive nutrients and  fibre to maintain a healthy gut microbiota and keep the horse in adequate health for reproduction. Proper functioning of the gastro-intestinal tract (GIT)  in horses is dependent on a broad range of micro-organisms and more than half of the energy requirement for their survival comes from the microbial fermentation occurring in their enlarged caecum and colon (Chaucheyras-Durand et al 2022). The bacterial populations resident in the various compartments of the horses intestinal tract vary greatly (Costa et al 2015) and there is more DNA in the bacteria located in the gastro-intestinal tract  than there is in the entire body. Because of this, having a healthy gut flora is critical to having a healthy immune system.

In modern times, our demands of horses for performance for our pleasure rather than their survival has led to their need for increased energy that cannot be provided from grass alone. Because of this, the intricacies of diet (in particular the consumption of starch, fibre and fat) has come under scrutiny. Equine feed manufacturers have looked for additional sources of starch, a carbohydrate and a natural component of grass that is ‘essential  to provide energy, fibre and a sense of fullness’ (Seitz 2022). Today, most horses and rapidly growing foals are commonly fed diets with >50% of total ration by weight in the form of grain ‘concentrates’ and carbohydrates from oats, maize, soya, barley and wheat. These grain based feeds contain high concentrations of soluble, easily fermentable starches but can be deficient in certain minerals and vitamins so getting an optimally balanced feed ‘right’ is difficult.

Too much of a good thing  

With advances in scientific knowledge, we now know that when a horse is exposed to surplus starch, the hydrogen ion concentration of their gut increases promoting  the production and absorption of lactic acid, acetate and propionate through the activity of fermentation (Ralston 1994). The process is quick, with lactic acid entering the bloodstream within 3 hours of feeding and calcium subsequently being excreted in the urine.  In order to combat this nutrient loss, the horses’ hormone system triggers the release of parathyroid hormone into the bloodstream, activating the release of stored calcium (to maintain optimal blood levels) but unfortunately causing  bone demineralisation. Clinically, the horse experiences health consequences of varying degrees including digestive diseases (eg: gastric ulcers, diarrhoea, colic or colitis), muscle dysfunction (eg: rhabdomyolysis (known as ‘tying up’), defective bone mineralization (expressed as increased incidence of stress fractures and developmental orthopaedic diseases), systemic diseases (such as laminitis, equine metabolic syndrome and obesity (Chaucheyras-Durand et al 2022) as well as potential causes of fatigue.

The ideal equine diet 

There is little equine focused research available on the benefits of individual nutrients (due to limited numbers in trials and their subsequent evaluation) of grain ‘concentrates’. But we do know that ingredient availability and quality is regularly influenced by market pressures. 

The table (fig 1) below outlines the sugar, starch and fibre components of the various ingredients commonly found in horse feeds. The optimal grain for equine nutrition with its efficient energy source through lower starch content (relative to other grains) and its high level of soluble fibre (relative to other grains) are oats.

Oats are highly digestible and do not require heat treatment or processing prior to feeding (unlike all other grains). They are the only grain that is easily digested raw and the least likely to cause insulin spikes and blood sugar fluctuations. Unfortunately, oats are not a ‘complete’ nutrient source as they are high in phosphorous and low in calcium. For adequate bone and muscle development as well as proper blood formation, oats must be balanced with additional vitamins and minerals.

The healing power of omegas and short chain fatty acids 

While grass provides optimal equine nutrition in its own right, the ‘curing process’ when making hay depletes the valuable omegas 3 and 6 intrinsic in grass. These ‘healing’ nutrients naturally protect the lining of the gastro-intestinal tract by increasing mucous production and alleviating ‘auto digestion’ (via hydrochloric acid). For horses, bacterial fermentation in the hind gut also results in the production of Short Chain Fatty Acids (SCFAs), namely acetic, proprionic and butyric acids. These SCFAs ‘cross talk’ with the gut immune system providing local immunity in the gut as well as protection of the respiratory system, the brain and other tissues against disease. In human medicine, it has been repeatedly established that a dysfunctional gut microbiome is associated with respiratory problems. This is evidenced by the fact that when gut disorders such as Irritable Bowel Syndrome  (IBD) or Coeliac disease exist in humans, they are commonly associated with a higher incidence of respiratory infections and related asthmatic like conditions. Barragry (2024) explores the relationship (Fig 2) between gut microbiome and the immune system's ability to support health and combat disease in cattle. A scenario mirrored in the equine.

The stabled horse should be provided with SCFAs daily to support proper functioning gut microbiome. This critical dietary consideration should ideally be provided in the form of flaxseed which has the highest ratio of omegas 3 and 6 (in the ideal ratio 4:1) in the plant world and is most suitable for the equine herbivore.

The health benefits of flaxseed for both humans and equines has been recognised as early as 3,000 BC. Flaxseed was used for various medicinal purposes such as the treatment of gastric disorders, as a soothing balm for inflammation and as a laxative (Judd, 1995). Horsemen (who relied heavily on their equines) and trainers (who sought optimal performance from their charges through natural means) also used flaxseed as a way to supplement the diet with omega-3’s and fibre to produce high quality proteins. Now, thirteen centuries later, we have research to substantiate the knowledge of our ancestors. The renowned German researcher of ‘fats’ and pioneer in human nutrition, Dr. Joanna Budwig, as early as the 1950’s reported that “the absence of highly unsaturated fatty acids causes many vital functions to weaken". Dr. Budwig’s life’s work focused on the dietary ‘imbalance’ between omega-3 and omega-6 fatty acids in humans has been a cornerstone to the exploration of the role of inflammation and the development of many diseases of the coronary, respiratory, metabolic and immune system.

The small seed of the flax plant is also an excellent source of high-quality protein (exceeding that of soybeans and fish oils) and potassium (a mineral that’s important for cell and muscle function). But, the true power of flaxseed lies in three key components: 

Omega-3 essential fatty acids – Also known as "good" fats, omegas enhance the oxygen usage of cells and in combination with alpha-linolenic acid (ALA) are anti-inflammatory in their effect within the body.

Lignans – Flaxseed contains 750 - 800 times more lignans than other plant foods (McCann 2007, Yan 2014). Lignans are a group of compounds with antioxidant properties which also contain plant oestrogen. Lignans are linked to a reduced risk of developing osteoporosis, heart disease and cancer.

Fibre - Flaxseed contains both the soluble and insoluble types of fibre essential for maintaining ‘gut’ health.

In equines, adding flaxseed to the diet has the immediate benefits of a shiny, healthy coat and fewer skin allergies. Consistent use of flaxseed has multiple long term benefits including strong hoof quality, improved joint health, reduced muscle soreness, faster healing of ulcers (Sonali et al 2008) and significantly impacts inflammation associated with chronic skin conditions (commonly known as ‘sweet itch’). In breeding stock, increased Omega-3 levels in mares’ milk leads to boosted immunity in foals with higher stallion fertility and improved conception rates in broodmares documented (Holmes, 2015).

How diet can influence performance 

It is easy to think that ‘providing more is better’ when it comes to using nutrition to support performance. But having excess levels of essential vitamins and minerals being processed by the horses’ sensitive gut has a direct impact on their behaviour and willingness to perform. Today, we have greater ‘choice’ at the feed store with a broad range of commercial feeding offerings available including mixes, mashes and supplements but the discerning horse owner can be forgiven for being overwhelmed by the range of diet options for every ailment and stage of life.

In modern times, despite advances in nutrition offerings, we have seen a falloff in performance (Fig 3). During the late 1960s, the U.S. Jockey Club stats noted that racehorses averaged 12 starts per year – a far cry from today's horses racing in the U.S. where the average of 3 ‘starts’ was highlighted by leading US Trainers in 2020 (www.ownerview.com). Unfortunately, this is not just a U.S. based problem, but a phenomenon noted worldwide. 

The first equine pelleted feed was formulated in the US by the Cistercian  monks in Gethsemani, Kentucky in 1957. Prior to this, all horses were fed ‘straights’ (primarily oats as their energy source and flaxseed as their protein source). My own understanding of the link between modern feeding practices and compromised performance since the 1960s has been curated off an understanding of “what was different” then, as well as a career of observations, clinical practice and scientific review. Fact is, the equine diet of the 1960s was lower in starch and high in fibre. It consisted of oats, minerals, and flaxseed as the “norm”. Hay was the preferred forage (Fig 4).

Today, soya (with one fifth of the omega 3 content of flaxseed) has practically replaced flaxseed as the protein source in equine nutrition. This small change has seen a significant drop in omega-3 and 6 (needed for prostaglandins) in the diet with consequential gastro-intestinal and joint issues. Other dietary changes include those recommended by the National Research Council (NRC) in 1978, who suggested doubling the recommended calcium levels for horses with a subsequent increase in levels of Osteochondrosis (OCD) and Osteopetrosis in the equine population (Krook and Maylin, 1989). Additional moisture in the diet too has led to excess mould formation in convenience feeds and with severe exposure causes liver damage (Buckley et al 2007). Stabled racehorses today mostly lack the nutritional protection afforded a previous generation of horses. The impact has been noted clinically in the widespread increase in equine gastric issues and as stated by J.E. Anthony “Racing fans are missing about half of what they once enjoyed in racing.”

The role of the gut bacteria in the prevention of disease

The gut microbiome begins populating and diversifying from the moment of birth. Though ‘sterile’ in utero, gut derived DNA immediately drives immune health with exposure to nutrition. Recent research suggests that the gut microbiome can be stimulated by using proven probiotics with a track record in enhancing gut health (Barragry 2024). But it is the protective power of SCFAs to allow ‘cross talk’ between the lungs and the gut microbiome that is critical to supporting horses through their lifespan. 

Nutrition using grain ‘concentrates’ is currently at approximately  99% saturation in today’s equine population so a return to feeding ‘straights’ is a swim against the tide of modernity. But, knowing the influence of nutrition on health, performance and longevity it falls on horse owners to be mindful of the consequential  impacts  such convenience feeds have on the gut microbiome and immune system. Random supplementation and high starch feeds are leading to dietary health issues such as gastric ulcers, hyperinsulinemia and  hyperlipaemia (obesity) as well as increased risk of laminitis . So trust your gut and keep it simple – a diet of oats, flaxseed, a multi-vitamin balancer and ad lib hay will not only meet your horses’ energy needs but will keep them happy and healthy too.

REFERENCES

Barragry. TB (2024) WEB https://www.veterinaryirelandjournal.com/focus/254-alternatives-to-antibiotics-probiotics-the-gut-microbiome-and-immunity

Buckley T, Creighton A, Fogarty (2007)  U. Analysis of Canadian and Irish forage, oats and commercially available equine concentrate feed for pathogenic fungi and mycotoxins. Ir Vet J. 2007 Apr 1;60(4):231-6. doi: 10.1186/2046-0481-60-4-231. PMID: 21851693; PMCID: PMC3113828.

Budwig, Dr. J (1903-2008) WEB https://www.budwig-stiftung.de/en/dr-johanna-budwig/her-research.html

Chaucheyras-Durand F, Sacy A, Karges K, Apper E (2022). Gastro-Intestinal Microbiota in Equines and Its Role in Health and Disease: The Black Box Opens. Microorganisms. 2022 Dec 19;10(12):2517. doi: 10.3390/microorganisms10122517. PMID: 36557769; PMCID: PMC9783266. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9783266/

Holmes, R (2015) Feeding for stallion fertility. WEB 

https://www.theirishfield.ie/feeding-for-stallion-fertility-172113/

Judd A (1995) Flax - Some historical considerations. Flaxseed and Human Nutrition, S C Cunnane, L U Thompson. AOCS Press, Champaign, IL 1995; 1–10 [Google Scholar]

Martinac, P (2018) What are the benefits of flaxseed  lignans?  WEB https://healthyeating.sfgate.com/benefits-flaxseed-lignans-8277.html

National Research Council. 1989. Nutrient Requirements of Horses. Washington D.C.: National Academy Press.

Ralston, S VMD, PhD, ACVN (1994) The effect of diet on acid-base status and mineral excretion in horses in the Journal of Equine Practice. Vol 16 No. 7. Dept of Animal Science, Rutgers University, New Brunswick, NJ 08903

Seitz, A  (2022) What to know about starch_Medically reviewed by Seitz, A - MS, RD, LDN, Nutrition — WEB https://www.medicalnewstoday.com/articles/what-is-starch#benefits

Sonali Joshi, Sagar Mandawgade, Vinam Mehta and Sadhana Sathaye (2008) Antiulcer Effect of Mammalian Lignan Precursors from Flaxseed, Pharmaceutical Biology, 46:5, 329-332, DOI: 10.1080/13880200801887732

The role of the lymphatic system in energy metabolism

Article by Peter Bollen, head nutritionist Cavalor

In recent years, focus has turned towards the emerging science of the lymphatic system. It is as important as the circulatory system (which includes the heart and the blood vessels), and is fundamental to the functioning of the body and central to the immune system, energy metabolism, detoxification and energy availability in the horse’s body.

A horse with a well-functioning lymphatic system can metabolise energy and clear metabolic waste more efficiently, leading to enhanced performance and faster recovery. 

So how can we tap into the benefits of an effective lymphatic system? Well, the first step is in understanding what it is. We might know that nutrients and oxygen are carried in the bloodstream towards our tissues, but what about how they are actually delivered to the cells?

This is where the lymphatic system comes in. Broadly speaking, it runs in parallel to the circulatory system and creates the point of delivery to the cells and tissues. The circulatory system carries the blood via arteries and vessels, which get smaller as they reach the muscle tissue as capillaries - where the wall is only one cell thick.  

This enables smaller molecules such as nutrients and oxygen to be pushed out of the capillaries and into the fluid around the cells - or lymph - while retaining larger cells like erythrocytes (red blood cells). 

The lymphatic system is an extensive network of vessels and nodes that transports lymphatic fluid around the body and it has two main functions:

1. Energy metabolism - transporting nutrients and oxygen to the cells

All the cells and tissues of a horse’s body are surrounded by a watery gel-like substance called interstitial fluid. This provides a medium for dissolved oxygen and nutrients to travel across to the cells. Lymph capillaries, carrying these substances, run through the interstitial fluid. The walls of these capillaries are also only one cell thick and have overlapping junctions, which make them highly permeable and allow easy transfer of materials.

In practical terms, this means the horse’s muscles and tissues get all the energy they require to carry out all their metabolic processes. As well as being responsible for giving cells the oxygen and nutrients they need, the interstitial fluid transports salts, hormones, neurotransmitters, coenzymes, amino acids, sugars and fatty acids around the body via the lymphatic system.

“A horse with a well-functioning lymphatic system can benefit from increased energy and enhanced performance, but without feeling too fresh or fizzy”

2. Detoxification: processing waste products

During the season, horses are placed under physiological demands and their body has a lot to process. In hard exercise and in races, their body will produce a lot of waste products. Their thin-walled lymph vessels also allow interstitial fluid into them to remove the waste products of cell metabolism (such as cell debris, bacteria, dead blood cells, pathogens, toxins, lactic acid and protein molecules) from each cell. This process is just as important as carrying necessary materials to the tissues to provide energy. 

These metabolic waste products are carried in the lymph away from the cells for detoxification. This is the term used for the continuous processes in the horse’s body to remove those waste products or metabolites that are naturally produced.

Detoxification takes place mainly in the liver, kidneys and intestines, so it is really important to ensure that those organs in the horse are healthy and functioning well. By supporting the liver and kidneys, you can help this breakdown process and allow the horse to better metabolise compounds that would otherwise be toxic if they remained in the body.

Gut health is also very important to the lymphatic system and detoxification, given that more than half of the lymphatic vessels of the horse are located within the gastrointestinal tract. 

Peristalsis (the natural contraction and relaxation of the gut wall) drives the return of lymph to the rest of the body. Movement in the gut is stimulated by food consumption (mainly long fibres) and is crucial to lymphatic system function as there is very limited muscular contraction in the horse’s lymphatic vessels themselves. This means it relies on passive forces from movement of other systems in the horse’s body as opposed to active muscle contractions.

Ensuring sufficient feed for a horse around the clock is crucial, not only for maintaining gut health, but to maintain a healthy immune system and detoxification process as well.

Lymphatic system and immune function

In addition to lymph and lymph vessels, the horse has around 8000 lymph nodes. These bundles of lymphoid tissue and proteins act as a filter for foreign substances that travel through the lymphatic fluid and contain lymphocytes (white blood cells) that help the body fight infection and disease. This means that the lymphatic system is also key to the functioning of the immune system.

As the lymph tissue approaches each lymph node, it slows down and collects in that area. Horses have so many lymph nodes that they are extremely susceptible to lymph node blockage. Lymph nodes can actually be felt or sometimes seen at various points around the horse’s body, particularly around the head and neck or when they are swollen.

Keep on moving

Movement is so important for horses, precisely because of the fact that there are no direct muscular contractions within the walls of the lymph vessels to promote the flow of lymph. The functioning of their lymphatic system relies on the force of movement of other structures in the body, such as the movement of the skin to apply pressure to the underlying tissues and stimulate the transport of lymph through the vessels.

In the modern day, racehorses can be stabled for longer periods of time. It is very common to see leg swelling, which has a very simple explanation in terms of the immune system. This principle of continuous movement being necessary applies especially to the legs, where this elastic movement of the skin is assisted by a pump mechanism in the hoof and fetlock joint. It is thought that this is the case due to there being no muscles in the lower limbs of the horse to aid the movement of lymph from this area.

Horses therefore need to move extensively and perhaps almost constantly (up to 16 hours per day) to keep the lymph circulating around the body, and standing still for too long significantly impairs the functioning of the lymphatic system.

Practical tips for a healthy lymphatic system

1. Turn horses out as much as possible  

Horses that are standing still for long periods of time are at risk of an impaired lymphatic system, which can impact the immune system, recovery time and ultimately performance. Turnout makes a happier horse and a healthier horse.

2. Cool down for at least 15 minutes after exercise

The period of time immediately after training is important for removal of metabolic waste products and keeping a horse moving after a hard training session stimulates the lymphatic system to continue to remove waste products from cells, which includes the removal of lactic acid. By cooling down properly after every session, you can significantly improve recovery times.

3. Consider feeding supplements that can directly benefit the lymphatic system

Functional herbal ingredients in innovative supplements can support lymphatic system function. Cleavers (Galium aparine) is known to bring benefits to the lymphatic system. Couch grass (Elymus repens), Nettle (Urtica dioica), and Dandelion (Taraxacum officinale) are all known to have purifying effects which can support metabolism and detoxification.

Even Lionel Messi, Usain Bolt or Iga Swiatek have picked up issues through their sporting careers, despite having elite support teams behind them. Unfortunately injuries do just happen, but with foresight, preparation and providing the best nutritional support to their horses, trainers will give themselves the greatest chance of avoiding yet another bad news phone call to an owner.

Hydrotherapy for performance - the benefits of water based conditioning - hydrotherapy as a mechanism for enhancing performance in the racehorse

What is hydrotherapy?

The historic use of water for therapeutic benefit in the equine industry has taken a leap in development in recent decades, from the humble use of cold hosing a swollen limb through to the development of water treadmills and water walkers for injury rehabilitation and performance development. Cold hosing and other forms of cooling localised areas of the body is more correctly termed cryotherapy—meaning, it aims to harness the benefits of reduction in temperature to treat mainly acute and oedemic injuries. By reducing temperature of the local area, for example, a distal portion of a limb, several key functional changes occur. First, local blood flow is reduced. This is especially useful if an open wound is involved; the precapillary sphincters constrict and direct blood away from the area. Secondly, there is evidence that nociceptors, involved in the perception of pain and sensory receptors located at the end of peripheral nerve endings can be temporarily suppressed with local application of cryotherapy. Following a brief summary of cryotherapy, this article is going to focus on hydrotherapy as a mechanism for enhancing performance in the racehorse, focusing on the specific parameters of fitness that can be targeted and thus improved.

• Fundamental properties of water

There are several fundamental principles of water that can be used as a recovery tool to facilitate optimum rehabilitation and ongoing performance improvement. When immersed in water, or made to move through water, the horse’s body, like the human, encounters a medium for which it is not designed, and locomotion is of limited efficiency. It is in fact the imposed limited efficiency that is useful in different training contexts—it forces the body to work harder than on dry ground, thus improving fitness and better preparing the horse’s body for future athletic tests. Similarly, the method of human altitude, or hypoxic training, is where the body will learn to produce the same amount of energy with a significantly lower available amount of oxygen and thus benefit at a later date in a competitive environment.

The effect of hydrostatic pressure increases as water depth increases.

First, and most important in an equine fitness protocol, is the viscosity of the water creating resistance; the resistance offered by water is greater than that experienced in locomotion on dry ground, therefore requiring greater overall effort to move through it. Exercising in water has shown to provide up to 15 times the resistance of exercising on land. This factor alone means that the trainer can achieve a far more challenging training environment without the horse experiencing the concussive forces on the limbs associated with high-end aerobic or anaerobic land based exercise, such as works on a gallops. Resistance also works indirectly at lower water levels whereby horses will choose to step over the water in a bid to avoid resistance. Therapists then utilise this to gain increased flexion at limb joints (further discussion of this throughout the article). Hydrostatic pressure is the pressure exerted on an object when immersed in water. Depth of immersion is an influential factor with greater depth correlating with greater pressure. Depending on the type of hydrotherapy system used, the benefits of hydrostatic pressure will vary. For example, greater hydrostatic pressure will be exerted when using a swimming lane with depths of up to two metres, as opposed to depths of 30-60cm of water on a treadmill. Application of hydrostatic pressure greatly benefits the recovery processes, acting in a similar way as compression bandages. The pressure reduces the formation of oedema, or swelling, and improves the elimination of muscular by-products such as lactic acid and carbon dioxide. Buoyancy is not utilised in the same way as it is in humans and small animal hydrotherapy, except in the use of swimming lanes; this is partly due to the obvious size difference and limitations associated with submerging a horse almost completely in water. Buoyancy is achieved when the weight of the fluid displaced by the body is equal, also accounting for the force of gravity on the body. To remain buoyant, the two forces must counterbalance one another. Once this balance occurs, the body is essentially weightless, allowing exercise without the impact of joint load experienced in land-based exercise. These properties act together during water-based exercise to produce the increased benefits to the horse’s fitness discussed in this article.

• What happens during a hydrotherapy session?

Horses are typically introduced to the hydrotherapy equipment to acclimate them and ensure they will be relaxed while exercising. It is important for the horse to establish a relaxed frame when working on the treadmill or in the hydrotherapy pool to prevent any stress-related or compensatory posture during the workout. As we know from land-based exercise, if a horse is stressed, they are likely to tire more quickly; so in order to utilise this workout, acclimation is beneficial. When using a treadmill, it is typical that the horse warms up on a dry treadmill prior to adding water. As with land-based exercise, a thorough warmup ensures adequate preparation of the horse’s muscles to be ready for harder work during the session.

• The bodily systems during exercise

During a hydrotherapy session, the horse’s different bodily systems will be affected in several ways. But essentially, the efficiency and smooth-running of these systems all contribute to overall performance quality, and any deficiencies will act as an overall limitation. The cardiovascular system is often considered to be the horse’s engine during locomotion, working with the respiratory system in concert to provide the horse with the oxygen needed for exercise as well as dispelling by-products. Working as a muscular pump, the heart delivers oxygen and nutrient-rich blood across the body via a network of blood vessels that develops further with long-term consistent exercise. Supplying this oxygen are the nasal structures; as obligate nasal breathers, horses must breathe through their noses. Flaring of nostrils and dilation of the horse’s larynx work to provide a greater cross-sectional area of space for oxygen uptake. When exercise begins, the previously oxygenated muscles begin to work and enter temporary oxygen debt. The cardiovascular and respiratory systems combat this by working harder to produce a continual supply of oxygenated blood by increasing the number of breaths taken per minute, thus increasing oxygen intake. During hydrotherapy exercise, the respiratory system will be required to deliver elevated levels of oxygen and removal of increased quantities of carbon dioxide. This is because the horse begins to work towards the higher levels of aerobic exercise. At rest, the horse will be taking in approximately 60 litres of air per minute; when moving towards moderately strenuous exercise, this can increase to as much as 2,250 litres of air per minute. From here the heart increases in beats per minute to keep up with this demand. When still working with oxygen the exercise is considered aerobic; when the horse reaches a speed or exercise intensity where they require greater oxygen than is available, the horse will begin working anaerobically. In a hydrotherapy setting, the treadmill can be considered more the equivalent of strength and conditioning training where heart rate does not rise significantly. On the contrary, swimming increases heart rate significantly without the concussive forces of traditional gallop work. This is when the horse is unable to utilise oxidative processes quickly enough—also known as maximum oxygen consumption (VO2max). Any further energy must be generated by anaerobic glycolysis. The horse cannot sustain long periods of anaerobic exercise, but instead the horse’s aerobic capacity becomes greater and thus delays onset of the anaerobic exercise.

Incidentally, horses also experience respiratory locomotor coupling in higher intensity canter and gallop work—a phenomenon that epitomises the efficiency of the horse as a performance animal. The stride and breath are in sync at a harmonious 1:1 ratio; they must lengthen their stride to increase their speed. From a fitness point of view, the respiratory system is often considered the horse’s limiting factor where minimal conditioning takes place of the related structures. Additionally, the horse’s respiratory system is highly specialised for exercise. This means that any damage to or deficiency of the respiratory system can have significant influence on overall performance. Unlike in the human, the horse’s resting heart rate does not lower with increased fitness; therefore, opportunities to measure fitness are reduced to monitoring during exercise and in the recovery phase.

Fitness testing methods may include blood-lactate tests, monitoring of respiratory and exercising heart rate, recovery rate from exercise—with the fitter the horse, the quicker the recovery rate. Like on dry treadmills, the controlled indoor nature of the hydrotherapy environment lends itself well to applying various fitness testing equipment as opposed to some of the environmental constraints often found in in-field exercise environments such as out on a gallops. In contrast, to the respiratory system, the horse’s muscular system has great potential for improvement, and targeted use of hydrotherapy can be hugely beneficial. …

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