Relationships between performance traits and osteochondrosis of the hock in Standardbred racehorses
Introduction: Equine owners and companies invest substantial resources into developing young Standardbred racehorses. However, their full potential is often not realized until later in their careers. Orthopedic health plays a crucial role in a horse's long-term performance and suitability for racing. Equine osteochondrosis (OC), a developmental orthopedic disease that occurs during a horse's first year, leads to abnormal articular cartilage and is prevalent among Standardbreds. While previous studies have investigated the relationship between OC and performance, a consensus has not been established.
Objective: To quantify the relationship between OC and nine performance traits using a cohort of 347 North American Standardbred horses.
Materials & Methods: Pre-existing data from radiographic examinations of the tarsi or hocks (a hindlimb anatomical region analogous to the human ankle) was used to identify horses as OC-affected (n=155) or healthy (n=192). Racing performance data was obtained from the United States Trotting Association. Linear and Poisson regression models were constructed to evaluate this data for relationships between OC and performance. A total of 30 performance related variables (e.g., age, gait, track) were evaluated for inclusion in the models through subset variable selection and goodness of fit as determined by Schwarz's Bayesian Information Criterion.
Results: Healthy horses demonstrated significantly faster mile times (p<0.001) and more finishes in the top three places (p=0.011) compared to their OC-affected counterparts; however, OC-affected horses raced more years (p=0.016) and had more lifetime starts (p=0.002). No significant association was detected between last quarter times, lifetime and annual earnings, consistency in race times over career, and number of lifetime wins.
Conclusion: The athletic ability of Standardbred racehorses may be limited as a consequence of OC, emphasizing the importance of implementing effective strategies for management and screening when breeding offspring with desired performance characteristics.