Radiographic changes in Thoroughbred yearlings. Part 2: Associations with racing performance.

The research paper studied the relationship between radiographic changes in Thoroughbred yearlings and their future racing performance. It was identified that specific changes, such as moderate or extreme palmar supracondylar lysis of the third metacarpus, enthesophyte formation on the proximal sesamoid bones, and dorsal medial intercarpal joint disease, significantly decrease the odds of the yearlings starting a race at ages 2 or 3 years.

Key Findings and Methodology

• The study made use of radiographs from routine pre- and post-sale examinations of 1162 Thoroughbred yearlings to identify individual radiographic changes. The performance of these yearlings was tracked during their 2nd and 3rd years of life. Performance was evaluated on criteria such as starting a race, the percentage of starts placed, and money earned.
• The investigation revealed that 946 (81%) of the yearlings started at least one race during their 2nd or 3rd years. Nonetheless, certain radiographic changes appeared to significantly decrease the likelihood of participation in a race. For instance, yearlings with moderate or severe palmar supracondylar lysis of the third metacarpus, enthesophyte formation on the proximal sesamoid bones, or dorsal medial intercarpal joint disease were three times less likely to take part in a race.
• Yearlings with proximal dorsal fragmentation of the first phalanx in the hind fetlock also showed a decreased racing propensity, with only 69% of the horses with this radiographic change starting a race.
• Another noteworthy finding was that yearlings with enthesophyte formation on the hind proximal sesamoid bones showed not only a decreased frequency of race participation but also a lower success rate when they did race. Compared with their peers, they placed in a smaller percentage of starts, earned less money, and had lower earnings per start.

Conclusions and Future Implications

• While not all radiographic changes observed in Thoroughbred yearlings were found to impact future racing performance, certain ones indeed showed a significant association with reduced performance.
• In light of these findings, it is recommended that the study’s results be used alongside clinical impressions of veterinarians experienced in examining radiographs of sale yearlings.
• Some of the results corroborated existing studies by identifying incidental findings, but others raised new concerns not previously reported for Thoroughbred sale yearlings, suggesting a need for continued research and heightened vigilance in early veterinary examinations of these horses.