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

/

Article by Dr Erwin Koenen and Richard Birnie

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

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

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

Wind Surgeries

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

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

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

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

  • Soft palate cautery, for the treatment of DDSP.

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


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

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

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

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

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

Genetic evaluation of WS 

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

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

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

Impact of genetic selection

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

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

Conclusion

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

References

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

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

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

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

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

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

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

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

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

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