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 stressmediated
influence of the adrenocortical system on the hypothalamicpituitary-
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 in 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
significantly (p < 0.05) lower spermatozoa concentrations 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.
