Novel serum biomarkers provide evidence for an involvement of the CCL3:CCL5 axis in fatal musculoskeletal injuries in Thoroughbred racehorses

Abstract Objective Fatal musculoskeletal (MSK) injuries in Thoroughbred (TB) racehorses adversely affect equine welfare, negatively impact public acceptance of horse racing, and cause severe economic losses for the racing industry. Biomarker assays predicting the risk of MSK injuries are currently not available. Our hypothesis was that immune system and inflammatory markers are indicators of fatal MSK injuries in TB racehorses. Methods Serum samples from TB racehorses with fatal (n = 44) and nonfatal injuries (63) were collected. Serum from 2- to 5-year-old TBs submitted for annual equine infectious anemia testing (n = 554) served as controls. All samples were measured for 12 immune and immune-regulatory markers using fluorescent bead–based multiplex assays. Results 4 serum biomarkers, C-C motif chemokine ligand 3 (CCL3), CCL5, CCL11, and soluble CD14, distinguished horses with fatal MSK injuries from controls. Two to 4 of these biomarkers were found in 70.4% of horses with fatal injuries, while 0 or 1 biomarker was positive in 99.1% of the controls. CCL3, CCL5, and CCL11 differed by fracture severity. CCL3:CCL5 ratios identified over 81% of the horses with fatal MSK injuries. Conclusions 4 novel serum biomarkers, CCL3, CCL5, CCL11, and soluble CD14, were identified in TB racehorses with fatal MSK injuries. CCL3:CCL5 ratios pointed to the mechanistic involvement of the CCL3:CCL5 axis in the pathogenesis of most MSK injuries. Clinical Relevance The novel serum MSK biomarkers are promising indicators for changes in normal bone remodeling and should be confirmed in prospective studies. Monitoring of these biomarkers can prompt timely clinical examination and advanced imaging to mitigate the risk for serious MSK injuries.