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

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• 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.

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.