Serum osteocalcin is associated with scintigraphic abnormalities in lame and clinically sound racehorses.

BACKGROUND: Musculoskeletal injury is a major welfare and economic challenge in racehorses, with stress-related bone injury contributing to training interruption and catastrophic failure. Advanced imaging modalities can detect early skeletal pathology but remain limited in routine screening environments. Circulating biomarkers of bone turnover may provide complementary indicators of skeletal remodelling but require validation against objective imaging findings. OBJECTIVES: Evaluate whether osteocalcin (OC) and C-terminal telopeptide of type I collagen (CTX), or the CTX/OC ratio, are associated with scintigraphic abnormalities and lameness status in racehorses and explore relationships with short-term adverse musculoskeletal outcomes. STUDY DESIGN: Prospective, observational case-control study. METHODS: Ninety-six racehorses were enrolled, including 48 lame horses referred for scintigraphy and 48 clinically sound controls. Serum OC and CTX concentrations were measured by ELISA at the time of scintigraphic examination. Scintigraphic scans were classified as no abnormality detected (NAD), moderately positive (mPOS) or strongly positive (sPOS). Associations were assessed using non-parametric tests, logistic regression and receiver operating characteristic analysis. Clinically sound horses were followed for 28 days to record adverse musculoskeletal outcomes. RESULTS: OC concentrations were higher in lame horses than in controls (mean difference 0.68 ng/mL, 95% CI 0.19-1.17) and differed across scintigraphic categories, with OC concentrations lower in NAD horses than in mPOS horses (mean difference 1.61 ng/mL, 95% CI 0.35-2.87). In the exploratory pooled injury analysis, higher OC concentrations were associated with musculoskeletal injury status (OR 9.75, 95% CI 2.82-49.38; AUC 0.75). In clinically sound horses, CTX and the CTX/OC ratio were not significantly associated with 28-day adverse musculoskeletal outcome. MAIN LIMITATIONS: Short follow-up duration, limited outcome events and potential workload-related confounding at sampling. CONCLUSIONS: Serum OC concentrations were associated with lameness status and scintigraphic severity. Bone turnover markers may provide complementary biological information alongside imaging but require validation in larger longitudinal studies.