Natural progression of tarsal osteochondrosis in Standardbred pacers and trotters

OBJECTIVE: To determine the natural progression of tarsal osteochondrosis (OC) in a cohort of Standardbred foals and assess the impact of gait preference (trotting vs. pacing). STUDY DESIGN: Longitudinal observational cohort study. ANIMALS: Client-owned Standardbred foals (n = 148). METHODS: analysis. Survival analysis was used to determine if lesion healing differed between groups over time. RESULTS: Of 148 horses, 103 (69.6%) had OC lesions at 2 months of age but only 32 (21.6%) still had OC lesions by 12 months. In 28 of these horses, the lesions had progressed to osteochondrosis dissecans (OCD). Of 71 horses with lesions that healed, 60 (84.5%) did so by 6 months of age. Gait was not associated with presence or absence of OC lesions or healing of lesions over time. Foals spent less than 1% of their observed time trotting or pacing. CONCLUSION: Tarsal OC lesions were prevalent in this cohort of young Standardbreds, and most lesions healed within the first few months of life. There was no evidence for direct biomechanical forces from movement at the pace or trot affecting the location of OCD fragment development. CLINICAL SIGNIFICANCE: The critical window for tarsal OC lesion healing was prior to 6 months of age and further investigation of risk factors present during this time frame is warranted.