Serum Osteocalcin and C-terminal telopeptides of type I collagen Correlated with Scintigraphic Abnormalities in Lame and Clinically Sound Racehorses.

Background: Musculoskeletal injuries are a major welfare and economic challenge in racehorses, with stress-related bone injuries contributing substantially to training interruption and catastrophic failure. Advanced imaging can detect early skeletal pathology but access is limited, creating a need for scalable indicators of bone health. Serum bone turnover markers may provide early signals of injury-related remodelling but require validation against objective imaging. Objectives: To determine whether serum osteocalcin (OC) and C-terminal telopeptides of type I collagen (CTX), individually or as the CTX/OC ratio, are associated with scintigraphic abnormalities, discriminate lame from clinically sound racehorses, and provide short-term predictive information for adverse outcomes. Study design: Prospective observational study with case–control comparisons. Methods: Ninety-six racehorses were enrolled, 48 lame horses referred for scintigraphy and 48 clinically sound controls. Serum OC and CTX were measured by ELISA concurrent with 99mTc-labelled bisphosphonate administration. Scans were classified as no abnormality detected (NAD), moderately positive (mPOS), or strongly positive (sPOS). Group comparisons,logistic regression, and receiver operating characteristic (ROC) analyses were performed. Short-term (28-day) outcomes were assessed in controls. Results: Mean OC was higher in lame than control horses (1.32 vs 0.39 ng/mL; P = 0.007), whereas CTX did not differ. Across all horses, OC was lower values in NAD horses (0.36 95% CI 0.02–0.71) than in mPOS (1.48,1.12–1.84) and sPOS (1.43,0.88–1.99;P < 0.0001). The CTX/OC ratio differed between NAD and positive scans (11.4 vs 6.0; P = 0.029). In injured horses, OC predicted injury (odds ratio ≈ 11.6, 95% CI 3.17–65.06; AUC = 0.75). CTX predicted short-term adverse outcomes in controls (odds ratio 2.21 per ng/mL; AUC = 0.76). Main limitations: Short follow-up duration, potential workload-related confounding at sampling and reliance on owner-reported outcomes. Conclusions: Serum OC is a robust indicator of scintigraphic bone pathology, while CTX is a potential predictor of short-term adverse outcomes.