A GPS-based investigation into the relationship between exercise irregularity and osteochondritis dissecans in Thoroughbred weanlings: A case-control study.

Osteochondritis dissecans (OCD) is a developmental orthopedic condition in young horses. Exercise and management affect OCD development, but the impact of exercise patterns during the 6-12 months growth period remains unclear. This study examined the association between OCD lesions in Thoroughbred foals and irregular exercise patterns. Forty foals wore halter-mounted Global Positioning System devices that recorded velocity every five seconds during turnout. Foals were routinely turned out for approximately 13 h daily, except on rainy days. Radiographs were taken at six and twelve months of age. Lesions were graded on a 0-4 scale and were converted into a 0-8 severity index. Speed data between 3 and 15 m/s were analyzed. Movement parameters, including mean velocity, velocity standard deviation, and the velocity outlier ratio (the proportion of values exceeding Q3 [third quartile] + 1.5 × IQR [interquartile range], indicating sudden accelerations or decelerations), were compared between OCD-positive and OCD-negative groups. Thirteen foals (32.5 %) were diagnosed with OCD. Total workload and mean velocity did not differ between groups, but the outlier ratio was significantly higher in OCD-positive foals. A combined metric incorporating body weight (Outlier Ratio × Weight Grade) was also higher in OCD-positive foals at 6 months (P < 0.05) and 12 months (P < 0.001). Radiographic scores and lesion progression were greater in OCD-positive foals. These results suggest that movement irregularity, especially in heavier foals, may contribute to OCD development. Monitoring irregular patterns could help identify at-risk foals and guide adjustments to exercise management during this critical period.