Hair cortisol concentrations and semen production of Bos taurus bulls.

Persistent increase on cortisol concentrations due to chronic stress can have detrimental effects on reproductive performance of animals. Blood cortisol concentrations have been used to investigate the stress-mediated influence of the adrenocortical system on the hypothalamic-pituitary-gonadal (HPG) axis. To date, cortisol assessment in hair samples has been reported as a validated method to evaluate hypothalamic-pituitary-adrenal (HPA) axis activity in humans and animals. The objectives of this study were to evaluate changes on hair cortisol concentrations relative to the beginning of semen production and the effects of hair cortisol concentrations on semen quality of bulls. Hair samples were obtained from 12 Holstein Frisian bulls (BW = 475 ± 57 kg; age= 13 ± 1 months) with a razor from the scapular region. Hair samples were collected at the time of arrival (P1) at the artificial insemination centers. After 30 days (P2), at the start of semen production, samples of new hair growth were collected from the same area. Hair samples were stored in dry tubes at room temperature until analysis. Hair was extracted by methanol and cortisol concentrations were determined by RIA. Mean hair cortisol concentrations in bulls at P1 and P2 were 4.5 ± 0.9 and 18.6 ± 6.5 pg/mg, respectively. The difference between the two sampling periods were significantly (P < 0.05) and the increase at P2 could be due to environmental and management changes. Moreover, it was observed that bulls with hair cortisol concentrations >10.0 pg/mg at P2 produced ejaculates with a significant (P < 0.05) lower spermatozoa concentration than bulls with hair cortisol concentrations < 5 pg/mg; thus, producing lower seminal doses. These results indicate that hair cortisol monitoring could be a useful tool for the evaluation of HPA axis activity in relation to the beginning of semen production in bulls. Evaluating the effect of HPA activity on the HPG axis could be important not only for their potential economic implications but also for implications concerning animal welfare