Gerald Leigh Lectures 2024 - Optimising Youngstock Growth and Development

Beaufort Cottage Educational Trust hosted the annual Gerald Leigh Memorial Lectures at Tattersalls in Newmarket on June 11th.  These lectures are in association with the Gerald Leigh Charitable Trust as a way of recognising Mr. Leigh’s achievements as a racehorse owner and breeder as well as continuing his passion for scientific knowledge and welfare of horses in the race industry and the equine industry as a whole. 

Dr. Chavatte-Palmer provided a very insightful and interesting talk on the influence of maternal and environmental factors during the prenatal period on athletic performance.  The lecture discussed the phenomenon of Developmental Origins of Health and Disease (DOHAD) which is demonstrated with the increasing evidence of the role in parental nutrition and environmental conditions, from periods preceding conception and throughout gestation, on phenotypic development in horses.  She described how the nutritional environment before birth can affect the postnatal performance of the offspring as it is believed that nutrients can alter the way genes are expressed resulting in developmental trajectories that have repercussions on postnatal development.  With a strong understanding and knowledge in DOHAD, nutritional strategies can be considered and developed to optimise youngstock growth and development.  This is an exciting field as further research will potentially allow veterinarians and breeders to work cooperatively to optimise athleticism as well as the wellbeing and health of foals and mares. 

Dr. Joe Pagan of the Kentucky Equine Research kindly visited from the U.S.A to discuss equine feeding management practices and equine nutrition in sports medicine. His first lecture discussed the effects of season on mare and foal nutrition.  Through various studies some conclusions could be made and these conclusions do appear to be a global trend.  It was found that colts are heavier and taller than fillies.  

After 1 month of age, fillies were fatter than colts.  Foals born in January and February were smaller at birth and grew more slowly in early life but by 150 days of age this lag disappeared.  In addition, mare weight changes and body condition scores were related to season and management factors, as winter-foaling mares lost weight and had lower body condition post foaling than spring-foaling mares. 

Dr. Pagan continued with a lecture on the right balance for optimal growth and development of youngstock.  Recent research has shown that the health of the offspring of overweight mares may also be compromised. In addition, studies have shown that excess maternal nutrition during pregnancy can alter glucose and lipid (fat) metabolism in foals until 160 days of age.  Another study reported a higher incidence of osteochondrosis (OC) in foals born to dams that were fed concentrates during gestation rather than forage. 

A more recent study on the nutrition of the mare during the last trimester and subsequent foal health revealed some interesting observations.  It was found that the growth of foals from 6-24 months of age was not affected by maternal diet and maternal undernutrition appeared to affect bone growth as foals from dams fed forage only had narrower cannon bones than foals from dams fed forage and barley.  In addition, it was found that overfeeding negatively affected yearlings from mares fed barley and forage more than yearlings from broodmares fed only forage.  

Finally, there was a decrease in insulin sensitivity and enhanced insulin levels suggesting insulin dysregulation in yearlings from mares fed both barley and forage and not yearlings from forage-only mares.  Another exciting field of research that will also lead to greater cooperation of breeders and veterinarians in providing good health and wellbeing to foals and mares.   

These lectures had the pleasure of hosting Paul Overton, who is an equine agronomist with a strong understanding of pasture management.  His passion for his area of expertise and in helping with improving management of studs was abundant as he outlined the aims of pasture management that included the need to provide safe grazing pastures from parasites, colic and grass sickness, atypical myopathy and other ailments as well as to provide a safe area to exercise horses of all ages.  In addition, he made clear that fresh leafy bite grass in the paddocks all year round is key.  

We were reminded of the fundamentals of good basic pasture management that included a removal programme for muck, providing a dense leafy grass sward, sharing and mixing the paddock use with other livestock (sheep and cattle) and moving horses to various paddocks around the stud to maximise rest of all paddocks. To optimise paddock health, it should be remembered that all paddock management follows the horses around the seed, be guided by the weather rather than the calendar and work quickly to maximise rest periods. Finally, good simple paddock and grassland management can help a multitude of issues and every marginal gain is helpful. 

Julian Dollar gave us an insight into a stud manager’s approach to soundness.  It was an integral part of the lecture programme as it provided the audience with another perspective of stud management. He made it clear that a variety of factors must be considered when breeding and raising sound horses but two main criteria is a strong team and an attention to detail. 

The team needed is one that is completely dedicated and passionate about their horses and should consist of a veterinary service, farriers, nutrition/feed and land management support. There must be a cooperative work ethic in order to provide the best all round management as possible. This team must strive for excellence and work on marginal gains.
A sound breeding and rearing programme starts with mating focusing on sound parents, especially the mare, to produce sound offspring.  It is important to work with mother nature rather than interfering with it, thus focusing on a healthy environment. This strategy must be flexible that will allow one to provide the horses with a quality paddock. 

The offspring should be between 55-60 kg and they should have a seamless transition from birth to exercise and living out.  In addition, the foals should be monitored and assessed closely in order to achieve timely and maximum beneficial interventions that may include selective surgeries.  Finally, it is believed that the perfect preparation for a yearling to go into training would be some controlled exercise combined with turnout the rest of the time. 

Professor Jacqui Matthews, the director of Austin Davis Biologics, provided some sobering information on parasites and their resistance in the United Kingdom.  She explained that intestinal worms are found in most grazing animals and most breeding premises are at high infection risk due to the presence of young animals grazing permanent pastures as well as having a history of interval deworming treatments. 

In addition, wormer resistance is being reported in all major parasitic worms of horses.  Therefore, it is vital to have control plans that include a risk-assessment approach.  Professor Matthews made it very clear that we need to be concerned regarding parasites and their resistance to wormers on UK studs and we need to act now.  She explained the action that is needed which includes evidence-based worm control.  This approach requires risk assessment that allows one to identify potential issues in the management, the avoidance of all horses regularly being treated, the assessment of wormer effectiveness as well as the effectiveness of interventions. 

With respect to the management, there are some principles behind reducing anthelmintic use.  Good pasture hygiene can substantially reduce infective egg and larval stages in the environment and the lowering of this pasture contamination decreases parasites acquired when grazing.  Pasture management must include: 

• Dung removal works! Full removal of dung at least once per week and place it away from pastures and water courses.  

• Maintain low stocking density 

• Rest pastures – ideally 12 months and avoid grazing foals on same paddocks every year 

• Consider grazing with ruminants between equine groups 

With respect to treatment, make informed choices by using various tests such as faecal worm egg counts, faecal egg count reduction test, antibody-based tests to identify worms, and other tests.  Ultimately, do not blindly treat horses without considering the reason for worming and assessing wormer effectiveness. 

Professor Matthews followed up with a second lecture on integrating diagnostics into sustainable equine helminth control programmes.  An integrated diagnostic-led control programme should consider: 

• Faecal egg worm count in late winter if grazing year-round.  Recommend treatment if 200 or more eggs per gram and select your anthelmintic according to its sensitivity. 

• Tapeworm test in spring to identify individuals with tapeworm burdens and treat infected individuals as these horses will contaminate the paddocks with cestode eggs. 

Late spring/early summer perform faecal egg worm count reduction test in order to assess anthelmintic effectiveness annually.  Worm all horses that have FEC of >200 eggs per gram.  Perform FEC test at day 0 and 14 days after treatment. Calculate the mean percentage.

• Reduction in FEC between 0 and day 14 post treatment. 

• In late summer/early autumn perform tapeworm test to identify individuals that have, over the summer grazing period, accumulated high tapeworm burdens which may put them at risk of colic  

In late autumn perform a small redworm test.  In low infection-risk situations, test in late autumn/winter to identify individuals that do not require treatment for small redworm.  Use in low-risk groups where owners usually apply all-group larvicidal treatments.

With good pasture management one can lower the selection for resistance, leading to a lowering the need for wormer treatments, a lowering in the proportion of horses that test positive and a lowering of paddock contamination; therefore, less horses are likely to be infected and more likely to have lower burdens. 

With his 20 years of buying and selling thoroughbred bloodstock, Jamie Railton gave us insights into the business of foal purchasing.  He discussed all of the variables that must be taken into account when selecting foals for purchase.  Skill and experience are needed in spotting the foal with the potential to increase in value because of its physical improvement and its pedigree.  He explained that a team of people are required as well as having a system to select foals; however, the system must be flexible and one must still want to continue to learn from the process and adapt and later the selection criteria. In addition, he discussed the need to reinvent oneself with the continuous change in the trends seen in the market. 

Dr. Rebecca Mouncey is a veterinary surgeon and post-doctoral research fellow, currently investigating early-life determinants of performance and economics of thoroughbred breeding.  

Dr. Mouncey discussed how musculoskeletal disease and injury remains the greatest barrier to thoroughbreds being retained within the industry and realising their maximum athletic potential, and is likely to have important economic consequences.  She explained that lameness/musculoskeletal injury and disease are the most common barriers to performance.  The causes of these conditions of developmental orthopaedic diseases are fractures and tendon/ligament injuries. 

By improving the foal’s/yearling’s strength to withstand training and resist injury, while avoiding trauma, one can help with the prevention of these diseases.  Unfortunately, there are still important knowledge gaps. It is possible to optimise musculoskeletal health during early-life with exposure during critical stages of growth and development that changes the distribution of cell types, alters metabolic function and ultimately altering the susceptibility and injury in adulthood.  

Postnatally the period of greatest plasticity, response to external stimuli/exposures is during periods of most rapid growth and development.  By 24 months of age, the horse is 96% mature bodyweight and 98% mature height and reached peak bone mass.  There must be a balance in early-life exercise and activity as too little will delay musculoskeletal development and too much will cause tissue damage and trauma.  We must always consider the animal’s growth, nutrition and exercise as a whole and not mutually exclusive.  

Abigail Kent MRCVS from Rossdales Veterinary Surgeons, presented an interesting lecture on the diagnosis and treatment of limb deformities in foals.  Dr. Kent is very knowledgeable in all aspects of equine elective and emergency surgery and has a particular interest in orthopaedics, specifically arthroscopy, angular limb correction and fracture repair.  

Limb deformities in foals are developmental orthopaedic conditions, that can be subdivided into 2 major groups: 1) angular limb deformities, in which there is deviation, primarily in the frontal plane, originating at a joint and/or growth plate and 2) flexural limb deformities, in which there is persistent hyperflexion or hyperextension of the limb. 

These conditions may be acquired or congenital and the aetiology is multifactorial.  Early appropriate intervention is the key to the best outcome. Angular limb deformities are relatively common in foals and strategies for management, including surgical techniques, are well established.  Early recognition, diagnosis and monitoring are essential in order to ensure optimal outcomes. 

In cases of severe deformities that fail to respond adequately to conservative approaches (restricted exercise, splints, corrective hoof trimming and shoeing) other treatments such as timely surgery may be used.  Transphyseal screws are effective for the corrections of both forelimb and hindlimb limb deformities.  Flexural limb deformities can be treated conservatively with the mainstays of limited controlled exercise, nursing care, manipulation of the foot with trimming/shoes, splinting/casting and pain management.

Surgical intervention is typically recommended when conservative treatment is not effective or for severe or rapidly worsening deformities. The goal of surgery is to release tension in the restrictive musculotendinous unit, allowing for greater stretch and more normal range of motion of the affected joint. 

In conclusion, all the contributors provided the participants a very interesting and illuminating day.  This event highlighted the lengths that all stakeholders and the veterinary profession are taking to constantly improve the health and wellbeing of the horses and the health of the race industry.  

7 Simple Rules for Parasite Control in Racing Yards

Article by James Gibbons

When Benjamin Franklin wrote, in 1789, ‘in this world nothing can be said to be certain, except death and taxes’, he could, perhaps, have added another certainty to his list – worms in horses. Unlike most other infectious diseases of horses, such as strangles or influenza—which infect a small number of horses relative to the entire horse population at any one time—worms are present in almost all horses all of the time.  This fact leads to two obvious conclusions: first, it is not possible to eradicate parasites and the threat of parasitic disease from our horses; second, worm control is vital in any environment where horses are kept.  

The threat posed by intestinal worms to racehorse performance has long been recognised by horsemen the world over. For many years, regular treatment with anthelmintic drugs (‘dewormers’) was the mainstay of worm control in racing yards, as it was in most in areas of horse breeding and production. The emergence of resistance to these deworming drugs (referred to as ‘anthelmintic resistance’), in the last 10 years in particular, has meant that such regular treatments may no longer be effective and may in fact make the resistance situation in the yard or farm worse. With this in mind, it is important that we consider how best to control worms while preserving the efficacy of the few deworming drugs available to us. This can be achieved using control programs comprised of drug- and non-drug control measures. This article sets out seven points/rules to consider and implement when developing such a worm control programme for racing yards. 

1. Know your enemy

It is not possible to draw up a parasite control program without considering which worms it is you are trying to control. The three main types of worms we are concerned with are strongyles (large and small redworms), ascarids (roundworms) and tapeworms. The role of tapeworms in equine intestinal disease is debated, but they appear to be linked to certain forms of colic when present in high numbers. Notably, there is no evidence of age-related immunity to tapeworms. Ascarids are a cause of disease in foals primarily and yearlings and so are likely to be of less concern in most racing yards. However, unlike redworms, which are transmitted almost exclusively at grass, ascarids can be transmitted in the stable; and ascarid eggs survive for years in the environment so that a single infected animal can infect other young horses for years to come.  

Redworms are the most important parasite of horses and are found in horses of all ages where they can cause anaemia, weight loss, ill-thrift and diarrhoea. Large redworms can burrow into the walls of blood vessels that supply blood to the gut causing a very severe form of colic.  Small red worms can lie dormant in the gut wall for extended periods then emerge en masse to cause an acute shock-like syndrome with severe diarrhoea, which is often fatal.  

Faecal egg count (FEC) testing will identify if redworms or ascarid eggs are present in your horse’s droppings and this, in turn, tells you that the adult worm of that species is present in your horse’s gut. Tapeworm eggs can be detected by FEC testing, but it is not the most reliable method for their detection as the shedding of these eggs is not consistent. As redworms are the most relevant worm present in most yards, most of the information in this article relates specifically to the control of redworms rather than ascarids or tapeworms.

2. Know your horses’ risk

All trainers pride themselves on their knowledge of almost every aspect of their horses’ anatomy and physiology, but not all could tell you which of their horses are at greater or lesser risk of worms. As mentioned above, all horses are likely to carry some worms, but the adult worm burden and the number of worm eggs shed in faeces is far greater in younger horses than in mature stock.  Most horses between the ages of 5 and 15 years will have a lower worm burden, and a lower risk of parasitic disease, than horses below this age due to a degree of age-related immunity. Foals and yearlings can carry particularly high worm burdens and shed large numbers of eggs into the environment to infect other horses. 

It follows that any yard with yearlings—two- or three-year-olds—will need a comprehensive worm control programme; while yards with older stock may get away with less strenuous controls. Horses over the age of 15 may also have higher worm burdens. And while these are unlikely to be in training, they may be used as a riding horse or companion animal and act as a potential source of infection for the string.

3. Know your yard’s weak points

It is not unusual for our lab to get a call from a racehorse trainer wishing to express their disbelief that the faecal egg count test from their horses has tested positive for redworm eggs despite their horses having no access to grass. In these situations, careful questioning as to how the yard operates will usually reveal the use of turn-out paddocks for a short period at some point during the week. Invariably, these are shared, often quite small, paddocks which host many horses over time; and so they are more likely to be contaminated with worm eggs.  

While the intention is for the horse to get ‘a pick of grass’, it may be that it is more ‘a pick of worms’ they are getting in such paddocks! As part of a worm control plan, it is important to first identify high-traffic areas, which may be a pinch-point for worm transmission.  Once identified, the key to reducing the worm burden on such paddocks is ideally through the removal of droppings. This can be a labour-intensive exercise, but it only needs to be done twice weekly rather than daily. And there are now more automated methods for cleaning paddocks than the more traditional wheelbarrow and spade!  

4. Identify high shedders 

FEC testing not only tells you what type of worm is present in your horse’s droppings but also how many eggs there are per gramme of faeces.  Repeated FEC testing allows you to build up a picture of the shedding patterns of the horses within your stable. Horses in racing yards should have FEC testing carried out every three months. It is generally accepted that the shedding of worm eggs in horses follows the 80/20 rule; that is, 20% of the horses shed 80% of the eggs.  

If these high shedders in the group can be identified, then targeted treatment of them may be more beneficial (and cost-effective) than blanket treatment of the entire group.    Horses with a strongyle egg count in excess of 250 eggs per gramme (EPG) on repeated testing may be considered high shedders and require more frequent egg counts and treatment.  It is important to state that this figure of 250EPG is not absolute, and the threshold above which animals are considered high shedders or requiring treatment should be set in conjunction with your vet. Worm eggs are not distributed evenly within the droppings, so when collecting samples for FEC testing, make sure to take at least three faecal balls—each from a different area of the pile. 

FEC testing can only detect egg-laying adult worms, but the egg count is not a reliable indicator of the adult worm burden of the horse, i.e. a horse with a high FEC does not necessarily have a greater worm burden than a horse with a lower FEC; but the horse with the high FEC is more significant in terms of worm transmission to other horses. Immature worms that may be present in the horse are not detected by FEC testing. In recent years, new tests have been developed that can detect antibodies to tapeworms and small redworm in blood and/or saliva. These tests are a useful addition to any worm control programme. Regardless of the type of test used, dewormers are still necessary as part of any worm control programme, in foals and yearlings in particular, but also in high-risk environments, and in order to control the disease risks posed to horses of all ages by large strongyles.  

5. Know which drugs work

While it might seem like there is an endless range of deworming products for horses on the market, the number of active ingredients in these products is very limited with only four drugs (fenbendazole, ivermectin, moxidectin and pyrantel) available for the treatment of redworms and ascarids. With such limited availability, and no prospect of new worm treatments entering the market anytime soon, it is vital that we use the existing drugs judiciously so as to preserve their effectiveness into the future.  

The threat posed by anthelmintic resistance is very real. Already fenbendazole resistance in redworms is widespread, and ivermectin/moxidectin resistance in ascarids is becoming more common. This means that there are only one or two effective treatments remaining for these resistant worms. While thoughts of anthelmintic resistance may not keep any racehorse trainer awake at night, we do expect that the deworming treatments we use to be effective, not least because they cost quite a lot of money!  The only way to determine if our treatments are indeed effective is to carry out a faecal egg count reduction test (FECRT). 

This test follows on from the FEC test; any horse with a FEC of 500EPG or more should be treated with a dewormer and have a follow-up FEC carried out 10–14 days after that treatment. The percentage reduction in egg numbers is calculated and should be greater than 90–95% (depending on the drug). Reductions less than this are suggestive of a resistance problem. Because of the existing resistance situation, FECRTs should be carried out before using fenbendazole to treat redworms or ivermectin/moxidectin to treat ascarids. Equally, if you have any suspicion that a deworming product is not working effectively in your yard, then a FECRT for that drug should be carried out to investigate this.   

6. Don’t overtreat

Aside from the risk of anthelmintic resistance development and the significant costs incurred by frequent or blanket deworming of all horses in the yard, such treatments can have other effects on the horse, which may ultimately impact performance. Research has shown that anthelmintic administration is associated with a decrease in the diversity and abundance of certain bacteria in the horse’s gut, which may impact digestion and other metabolic processes. 

In humans, changes in the composition of the gut bacterial population have been shown to impact physiology, immunity and behaviour; and, while the structure of the gut may differ greatly between human and horses, there is no reason to believe the equine gut bacteria do not play a similarly important role in horse health. In recent years, the role of parasites in human health has been revaluated. And while they are still recognised as an important cause of disease, it is also accepted that they can play a beneficial role in the development of immunity and the prevention of some diseases. While we don’t have similar evidence of a benefit to horse health from parasites, it is not impossible that such benefits do really exist.  

A study of standardbred trotters in Denmark in 2011 found that horses with higher egg counts had better race finishing position than those with lower egg counts. So,  the presence of parasites does not always lead to poor performance! It was standard practice, in some racing yards, to deworm horses every eight weeks, but this seems excessive when one considers the biology of the worms involved. The small redworms take approximately eight weeks to develop to maturity in the horse, while the large redworms take approximately six months to do so. Treatment every eight weeks could only be justified if there were evidence of overwhelming worm exposure on an ongoing basis—something which is unlikely in a modern racing yard. Even if that were the case, other non-pharmaceutical controls would be necessary to get the situation under control.

7. Manage new arrivals

One of the challenges of worm control in a racing yard is the constant turnover of horses with some leaving the yard for rest or recovery from injury, others returning from such breaks and new horses joining the yard. When a horse leaves the yard, they leave the worm control programme as well. Evem if the yard’s deworming programme is followed while they are away, the risk factors in their new environment may be totally different and require an entirely different approach to treatment. More worrisome, the arrival of new horses or the return of others also risks the introduction of new or resistant parasites to the yard. In order to minimise this risk, all new arrivals should be isolated, tested and treated. Ideally, all new arrivals would be isolated for two weeks while a FECRT is carried out to ensure treatment has been effective.  

This may not be practical in all yards, but an isolation of period of at least three days after deworming should be observed to ensure all worms are shed before the horse joins the group. Treatment without isolation is not recommended as treated horses can shed viable eggs for a few days after deworming. There may be a temptation to let horses out to turnout paddocks for exercise or grass during the isolation period, but we have seen cases where this has led to the introduction of new parasites to the yard despite the horse being treated before it was turned out.   

There was a time when parasite control in racing yards was relatively simple and relied primarily on the regular use of deworming drugs. As with many aspects of horse racing, what was once considered acceptable is no longer so. Effective parasite control is not as simple anymore, and an overall plan designed to meet the needs of the individual yard is required. That is not to say that any trainer should be daunted by the prospect of drawing up such a plan. The seven points discussed here provide a basis to work from and your vet and laboratory are well placed to assist in building on this.