Influence of age and sex in serum osteocalcin levels in thoroughbred horses

In this study, we assessed the potential value of free serum osteocalcin or bone gla protein (BGP), the most abundant non collagenous matrix protein f ound in bone and dentin, to reflect changes of bone turnover in thoroughbre d horses. Levels of osteocalcin were analyzed in serum samples of 54 clinic ally normal animals divided into three groups (A, B, C) according to age: 8 , 16-18 and 24-36 months, in order to determine the standard for young hors es of different age and sex. Serum BGP was measured by an in-house develope d double antibody radioimmunoassay using bovine antigen. The mean BGP level s (ng/ml) were 45.65 +/- 11.69; 33.65 +/- 16.65; 15.08 +/- 6.70 respectivel y for groups A, B and C; statistically significant differences were found b etween groups (A vs B and C; B vs C). Difference between males and females was found significant in group C with higher values in the females: 18.75 /- 5.00 against 14.43 +/- 10.47 in the males. This can be considered a sex related effect on BGP serum levels after the onset of puberty. Correlation coefficient between age and serum BGP for females and males wer e r = -0.598 (P < 0.001) and r = -00.807 (P < 0.001) respectively. A signif icant negative linear relationship could be established between these two p arameters in males during the growth period. The regression equation betwee n serum BGP and age for males was (month of age = 65.14-1.68 . BGP). In the female group the gestation and lactation are variables that lower the corr elation coefficient between age and serum BGP levels. These results suggest that serum BGP decreases in thoroughbred horses during the growth period, and significant differences between sexes were found only after the onset o f puberty.