THE EFFECT OF REPEATED BOAR EXPOSURE ON CORTISOL SECRETION AND REPRODUCTION IN GILTS

It has been proposed that short-term activation of the hypothalamo-pit uitary adrenal axis, with a consequent increase in the secretion of co rtisol, may disrupt the endocrine events prior to ovulation and thereb y impair reproduction in females. We investigated this concept in gilt s in which oestrus was detected by introduction to boars, where intens e physical contact is possible, or by applying pressure to the back of gilts (back-pressure test) during fence-line exposure to boars, where intense physical contact is prohibited. We expected that there would be a greater release of cortisol and that reproduction would be inhibi ted in gilts introduced to boars compared to gilts in which the back-p ressure test was used. As expected, introduction of gilts to boars res ulted in a significant transient increase in plasma concentrations of cortisol while there was no significant effect of using the back-press ure test on plasma cortisol. Nevertheless, introduction of gilts to bo ars did not impair reproduction and there was no effect of method of d etecting oestrus on duration of oestrus, sexual receptivity, fertility or fecundity. The length of the oestrous cycle was decreased and ovul ation rate increased in gilts that were introduced to boars compared t o gilts that underwent the back-pressure test, indicating that introdu ction of gilts to boars may have stimulated these aspects of reproduct ion. These stimulatory effects may have been due to an increased expos ure of gilts to sexual behaviour and stimuli from boars when introduce d to boars and/or to stimulatory effects of the hypothalamo-pituitary adrenal axis on some aspects of reproduction. (C) 1998 Elsevier Scienc e B.V.