Impact of periarticular osteophytes of the distal tarsus diagnosed in nonlame yearling Standardbred horses on racing performance

Objective: The aim of this study was to identify the radiographic prevalence of periarticular osteophytes of the distal tarsus in nonlame yearling Standardbred horses, and to evaluate its potential impact on race performance. Study design: Cross-sectional cohort study. Animals: Client-owned yearling Standardbred horses (n = 416). Methods: Bilateral tarsal radiographs were available from all horses for review. Osteophytes were measured on radiographs using clinical visualization software and categorized by size. Racing records were obtained from the United States Trotting Association. Regression analysis was used to determine associations between presence or size of periarticular osteophytes and performance parameters with sex and gait covariates. Results: Of 416 Standardbred yearlings without clinical lameness, 113 (27.1%) had distal tarsal periarticular osteophytes. Regression analyses revealed few associations between the presence of periarticular osteophytes and performance parameters. Affected horses had fewer starts at 4 years of age (incident rate ratio [IRR] 0.92, p =.01) and fewer lifetime starts (IRR 0.95, p =.003), but the effect size was small. Within the affected group, osteophyte size was only associated with number of starts at 3 (IRR 0.67, p <.0001). Sex and gait affected many performance parameters. Conclusion: The prevalence of distal tarsal periarticular osteophytes was similar to that in other breeds. Periarticular osteophytes of the distal tarsus appeared to be a largely incidental finding in nonlame yearling Standardbreds intended for harness racing. Clinical significance: Distal tarsal periarticular osteophytes in young, nonlame Standardbred horses should affect racing potential only minimally. This is in contrast to reports from other disciplines.