Assessment of synovial fluid biomarkers in healthy foals and in foals with tarsocrural osteochondrosis.

Although alterations in biomarkers of cartilage turnover in synovial fluid (SF) have been demonstrated in horses with osteochondrosis (OC), there have been few investigations of such alterations in animals <1 year old. In this study tarsocrural SF samples from foals aged 18, 22 and 52 weeks of age were assessed for: (1) 'turnover' biomarkers of type II collagen (CPII and C2C) and proteoglycan (CS846 and glycosaminoglycans [GAG]); (2) matrix metalloproteinase (MMP) activity; (3) insulin-like growth factor (IGF)-1; (4) transforming growth factor (TGF)-β1; (5) prostaglandin (PG) E(2); and (6) leukotriene B(4). Using a linear mixed model, the concentration of biomarkers was compared between animals that developed or did not develop radiographic evidence of OC at 24 or 48 weeks of age. The CPII:C2C ratio tended to be higher in OC-affected joints compared to controls at all ages, and this difference was statistically significant at 22 weeks of age. The concentrations of CS846 and IGF-1, and the CS846:GAG ratio were reduced in OC-affected joints relative to controls at 18 weeks of age only. At 52 weeks of age, the PGE(2) concentration was lower in joints with OC. Overall, there appears to be a consistent anabolic shift in type II collagen turnover in juvenile joints affected by OC. Aberrant proteoglycan turnover is not a hallmark of the late repair of this lesion but reduced concentrations of IGF-1 in SF may be associated with early-stage lesions.