Steroid implants and markers of bone turnover in steers

________________________________________________________________________________ Abstract Steroidal implants are used extensively in beef cattle management to take advantage of welldocumented improvements in growth performance and efficiency. In addition to muscle growth, steroids bring about changes in bone and cartilage formation, hastening bone ageing. The current study was designed to test the hypothesis that recently identified indicators of bone and cartilage turnover could be detected in the peripheral circulation, and that these markers might reflect accelerated ageing effects of the widely used steroidal implants, trenbolone acetate (TBA) and estradiol-17β (E2). Thirty-two crossbred yearling steers were given one of four treatments to determine whether these markers of bone turnover could be detected and reflect steroid-induced bone maturity in the periphery: non-implanted controls; 25.7 mg estradiol-17β (E2); 120 mg trenbolone acetate (TBA); or 120 mg TBA and 24 mg E2 (T+E). Blood was collected on days 0, 7, 14 and 28 and serum analysed by ELISA for concentrations of IGF-I, osteocalcin, C-terminal telopeptides of Type I collagen (CTX-I) and C-terminal telopeptides of Type II collagen (CTX-II), as markers of the somatotropic-endocrine axis, bone formation, bone resorption and cartilage resorption, respectively. Circulating IGF-I was greater in E2 or T+E treated steers than controls on days 7 and 14. Osteocalcin was unaffected by treatment, but increased from day 0 on days 7, 14 and 28. Treatment did not affect CTX-I. However, CTX-II was elevated in the treated animals as opposed to the controls. Although these markers of bone and cartilage turnover are detectable, results suggest that implant-induced changes are not evident in the circulatory system. _______________________________________________________________________________________