Influence of heat stress or feed restriction on plasma progesterone, oestradiol-17 beta, LH, FSH, prolactin and cortisol in Holstein heifers

The aim of the study was to compare the effects of heat stress and feed res triction on hormonal secretion (progesterone, oestradiol-17 beta, luteinizi ng hormone, follicle-stimulating hormone, prolactin and cortisol) in Holste in heifers. Ten pubertal heifers were divided into two groups of five (A an d B) and housed in climatic chambers. After a pre-experimental period, the heifers were synchronised for oestrus and monitored for three (group B) or four (group A) consecutive oestrus cycles (OC). In the first OC, both group s were maintained under thermal comfort (TC) and fed on an ad libitum basis . In the second OC, group A was maintained under TC whereas group B was exp osed to high air temperatures (HAT); both groups were fed on an ad libitum basis. In the third OC and until day 17 of the fourth OC, group A was kept under TC and fed a restricted diet (the same ration ingested by group B und er HAT). At the end of HAT exposure, group B was removed from the study. Ex posure to HAT caused development of ovarian cysts in two heifers, an increa se in plasma concentrations of prolactin, a decrease in concentrations of c ortisol and progesterone, and a 23% reduction in dry matter intake. Feed re striction did not modify any of the parameters considered. Results of this study indicated that the effects of HAT on the above parameters are not alt ered by a reduction in feed intake. (C) 2001 Elsevier Science B.V. All righ ts reserved.