Case-control study of high-speed exercise history of Thoroughbred and Quarter Horse racehorses that died related to a complete scapular fracture.

This study examines the relationship between exercise patterns and the risk of scapular fracture in Thoroughbred (TB) and Quarter Horse (QH) racehorses. The research investigates the hypothesis that identifying certain exercise history patterns can lead to more effective prevention of catastrophic injuries in racehorses such as complete scapular fractures.

Methodology

• The study retrospectively analysed high-speed exercise histories of 65 Thoroughbreds and 26 Quarter Horses. Each of these racehorses had a complete scapular fracture, and the data of these cases were compared with two matched control racehorses.
• The exercise variables were taken from the horses’ lifetime race and official timed workout reports. The associations between these exercise variables and the occurrence of scapular fractures were assessed using conditional logistic regression.

Results

• The data pointed out that Thoroughbreds with a scapular fracture had a greater number of workouts, combined works and races, and also longer mean event distances compared to Quarter Horses with the same injury.
• In contrast, Quarter Horses worked less frequently and accumulated less distance at a higher speed than the TBs. However, no marked differences were observed between the breeds in terms of length and number of races in their career, time taken between races, or lay-up variables for horses that had at least one lay-up.
• Regardless of the breed, horses that had experienced a scapular fracture typically had fewer events, lesser recent accumulated distance, and fewer active days in training than control horses.
• Furthermore, it was identified that among the subset of TBs with more than 10 events since lay-up, those with a fracture had a longer active career than controls.
• Among QHs that had experienced a lay-up, both total and mean lay-up times were found to be greater for horses with a fracture as compared to control horses.

Conclusion

• Evidence from the study suggests that odds of scapular fracture were greater for TBs that had not yet raced and lower for QHs with more race events.
• Racehorses in the early stages of high-speed training, particularly those lagging behind their training cohort, should be monitored for signs of scapular stress remodelling.
• Similarly, Thoroughbreds with a longer period of high-speed training and Quarter Horses that had a longer lay-up than their training cohort were also identified as having a greater risk of scapular fractures.