Bacterial gut diversity - new research!

Words Alysen Miller

The link between a healthy gut and overall health in both humans and equines has long been promoted by scientists and veterinarians.

Now a new study by the University of Surrey provides the clearest link yet between gut health and athletic performance in Thoroughbred racehorses, and identifies a “critical window” for immunological development which may provide owners and trainers with a glimpse into a racehorse’s future success on the track.

The study, published in the journal Scientific Reports, found that the composition of gut bacteria at just one month old can predict future athletic performance – measured by BHA official ratings (OR), earnings and placings – with a greater diversity of gut bacteria associated with better performance metrics. The study also found that foals with lower bacterial diversity at just 28 days old had a significantly higher risk of respiratory diseases and even soft tissue injuries later in life.

The study’s lead, Professor Chris Proudman, has dedicated his career to equine gastrointestinal health; first as a veterinary surgeon specialising in the clinical management of colic cases and latterly as head of the University of Surrey’s School of Veterinary Medicine. Since stepping down as Head of School last year, he now devotes his time to horse gut research. “I’ve got a small group of people investigating various aspects of intestinal health in horses, particularly around bacterial populations associated with health and disease,” he tells Trainer Magazine. The latest study is the culmination of more than a decade’s worth of research into the influence of gut bacteria on the development of immunological competence and susceptibility to disease. “I was aware of emerging evidence in the human field to suggest that these early life gut bacteria are really important in priming the immunological system and effectively setting up humans or animals for a healthy life in the future,” he says. “So with funding from ALBORADA Trust [the study’s sponsor], this was an opportunity to look in more detail at the impact of early life experiences in foals.”

So how does gut bacterial community structure in the first few months of life predict the risk of specific diseases and athletic performance in racehorses? To answer that question, Professor Proudman and his team performed DNA sequencing on faecal samples from 52 Thoroughbred foals born across five stud farms in 2018. These samples were collected at nine sample points within the first year of the foals’ lives: at 2, 8, 14, 28, 60, 90, 180, 272 and 365 days old. In addition, weekly written or verbal health updates were obtained for all horses reporting any veterinary investigation or treatment for orthopaedic, soft tissue, respiratory or gastrointestinal disease or injury. The researchers then compared this with the horses’ athletic performances at 2 and 3 years old: finishing position and OR were obtained after every race start, while total prize money earnings and cumulative performance metrics (total starts, total placings, total wins) were collected for all race starts until the end of December 2021.

The findings were striking. Not only did researchers observe that the athletic performance of the foals was positively associated with higher faecal bacterial diversity at just one month old, they also identified that a higher abundance of the bacteria Anaeroplasmataceae was associated with a higher OR, and increased levels of the bacteria Bacillaceae at 28 days old were linked to higher race placings. “We weren’t necessarily expecting to see [a correlation between gut health and performance], so the fact that early life gut bacteria influenced athletic performance came as a bit of a surprise to us,” admits Professor Proudman. “But it is consistent with the whole picture around health,” he continues. Professor Proudman is hesitant to attribute too much importance to the precise identity of the bacteria that were present: “I think what is probably more important is what those bacteria are doing, the mechanism by which those bacteria are affecting the animal, and we don’t understand that at the moment,” he suggests. The two different bacteria identified “could potentially be doing the same thing or they could be doing different things,” he continues. “It’s just an indication that there are bacteria that have a beneficial effect.” Further study is planned to try to identify in more granular detail the precise bacteria that are important to a horse’s performance. Nevertheless, the findings are the best evidence to date of a causal link between gut health and athletic aptitude: “This is really hard science that there are measurable beneficial effects both in terms of health and in terms of performance associated with diversity of the gut bacteria, and also with species of bacteria if they are present at this very early stage in life,” says Professor Proudman.

The concept of a “critical window” for immunological development is not new. Many lines of evidence point to the existence of such a period, during which time the immune system can be “trained” to tolerate particular microbes, and thus avoid later destructive immunopathology associated with these same microbes. While the window has been demonstrated in laboratory animals, “humans studies haven’t really been able to nail down the time period,” says Professor Proudman. “Most of the human studies state that it’s somewhere between birth and weaning,” he continues. “That’s a window of about 6-8 months for a lot of human babies. Because we were able to sample our foals very frequently during the first six months of life, we’ve been able to identify with a reasonable degree of accuracy a critical window for performance that happens very, very early – the first 28 days,” says Professor Proudman. Again, Professor Proudman is cautious about drawing a hard line at the 28-day mark: “I wouldn’t obsess about 28 days exactly – I think this is just telling us there’s something really early in life, in the first few weeks, which is the critical period,” he says.

It is not only future athletic performance which is determined within this critical window; higher bacterial diversity at 28 days old was significantly associated with a reduced risk of respiratory diseases later in life. “It’s likely that what we’re looking at here is the process of immunological priming,” explains Professor Proudman. Immunological priming is the process by which a host improves its immune defences following an initial pathogenic exposure, leading to better protection after a subsequent infection with the same – or different – pathogens. Or to put it another way: “When the horse (or any animal) is first born, the body has to learn to recognise the difference between the ‘self’ and the ‘non-self’ – the potential organisms, bacteria and viruses that are trying to invade the animal. And then it learns to fight those off,” explains Professor Proudman. “But there’s an initial learning period – this so-called period of immunological priming – and it seems that bacterial composition of the gut is important because the gut is a really important interface between the animal and the external environment,” he continues. “And that’s where this immunological priming takes place.

“This is the area in which most of the human research has been done, particularly around respiratory disease. And there’s really good evidence in both human and animal models that the gut microbiota have a significant impact on the development of the early immune system very early in life. So it’s highly likely, although we didn’t look at it specifically in our study, that this is an immunological effect that we’re seeing.”

Researchers also identified a positive association between the abundance of the particular bacteria Streptococcaceae and Moraxellaceae and the risk of soft-tissue health events such as infected wounds, cellulitis and abscesses. “There are specific bacteria that we know cause soft tissue infections,” explains Professor Proudman. “And again, it’s that resistance to bacterial infection that is mediated by the immune system.”

But where do these bacteria come from, and what could the answer mean for the way racehorses are bred and reared? The answer appears to be partly nature and partly nurture. Your gut is full of trillions of bacteria and other microbes help you digest food and support immune, heart and brain health. These are known collectively as the microbiome. It has long been thought that foals (and humans) are first exposed to microbes when they pass through their mother’s birth canal. However, evidence from human studies suggests that babies may come into contact with some microbes while inside the womb. A follow-on study by Professor Proudman’s team, scheduled to commence in early 2025, aims to identify where exactly the bacteria come from by tracking pairs of mares and their foals. But for now, “it’s a question that we don’t currently have an answer to,” concedes Professor Proudman. “People have had theories and you can make plausible explanations of where they might come from. Extrapolating from humans, the suggestion is that a lot of those bacteria actually come from faecal contamination of the foal by the mother. But there’s some really intriguing evidence around breast milk, for example.”

Certainly, the gut microbiome continues to diversify as the foal matures, suggesting environmental factors play a role. This includes the food they eat as well as factors such as whether antibiotics are administered. Ah, antibiotics. The epidemiological elephant in the room. Any discussion around antibiotics inevitably leads back to antibiotic resistance. Also known as antimicrobial resistance (AMR), antibiotic resistance is when bacteria change so antibiotic medicines can't kill them or stop their growth. This makes certain bacterial infections difficult to treat. AMR is caused by the misuse and overuse of antimicrobials in humans, animals and plants. The World Health Organisation has identified AMR as one of the top global public health and development threats. (It is estimated that bacterial AMR was directly responsible for 1.27 million global deaths in 2019 and contributed to 4.95 million deaths.) So what does this have to do with racehorses? Professor Proudman’s team also investigated the long-term impact of foals receiving antibiotics during the first month of life. It was found that these foals had significantly lower faecal bacterial diversity at 28 days old compared to other foals who did not receive such treatments. Further analysis revealed that these foals won significantly lower prize money earnings (an indicator of athletic performance) in their subsequent racing careers. In addition, foals who received antibiotics during their first 28 days of life had a significantly increased rate of developing a respiratory disease compared to their counterparts.

While the study does not necessarily demonstrate causality, “we can demonstrate an association between an event, in this case the composition of the microbial community in the gut and a downstream outcome which is either a health related event, or performance,” explains Professor Proudman. “We go to pains in the paper to say we can’t prove that it’s causal,” he emphasises. “However, as we say in the paper, we do believe that a causal association is a credible interpretation of our data. And one of the strongest reasons for this is simply the timeline. We’ve got something happening early in the animal’s life that is then leading to something that happens much later on in the animal’s life. A plausible explanation is that the antibiotics are hitting the gut bacterial population, disrupting it, and then that, in turn, is disrupting immunological development, which leads to an animal that is more susceptible to respiratory disease.”

While it is recognised that antibiotics play a vital role in treating infections and protecting the long-term health of foals, Professor Proudman is clear that they need to be used responsibly: “[AMR] can develop in animals and then transfer to humans and vice versa. So it helps everybody to minimise the use of antibiotics. Even accepting that some foals need to have antibiotics for medical reasons, if there’s something we can do to minimise the damage that those antibiotics do to gut bacteria, that's the question we’re asking.”

So what are the implications of this research for the racing and breeding industries? “I suspect the gut microbiome is only part of the story,” says Professor Proudman. “There are lots of other factors [that contribute to a horse’s health and performance], such as genetics, environment, and its response to training. I don’t think we are anywhere near a situation yet where we’ll be able to screen horses for potential on the basis of their bacterial communities,” he says. “However, I think there are some really simple things that the racing industry and, in particular, the breeding industry could take on board which could help them.” To that end, a follow-on study, funded by the Horserace Betting Levy Board, will look for potential probiotic bacteria that can be fed to foals in the form of feed supplements that will then colonise their intestine and produce beneficial effects. “In the same way that you could go to the supermarket and get yoghurt with probiotic bacteria in them, we’re identifying bacteria which might do the same thing for horses; in particular, for foals,” explains Professor Proudman. His team is already working with various players in the feed and supplement industries. “There might be some new products in development within the next few years directly arising from this research,” he hints.

“The Thoroughbred breeding industry is very traditional,” Professor Proudman continues. “And I think there probably has been an under-recognition of the genetic contribution of gut bacteria to foals’ health and ultimately their performance. It’s quite theoretical at the moment and we need to explore it in more detail. But certainly I think in the future, if stud farms have mares that have good, healthy gut bacteria, we think that’s going to be passed on to foals. So, it’s another aspect of racehorse genetics that has value as a commercial proposition.”

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.