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 restriction on hormonal secretion (progesterone, oestradiol-17 beta, luteinizing hormone, follicle-stimulating hormone, prolactin and cortisol) in Holstein heifers. Ten pubertal heifers were divided into two groups of five (A and 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 groups 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 exposed 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 under HAT). At the end of HAT exposure, group B was removed from the study. Exposure to HAT caused development of ovarian cysts in two heifers, an increase in plasma concentrations of prolactin, a decrease in concentrations of cortisol and progesterone, and a 23% reduction in dry matter intake. Feed restriction did not modify any of the parameters considered. Results of this study indicated that the effects of HAT on the above parameters are not altered by a reduction in feed intake. (C) 2001 Elsevier Science B.V. All rights reserved.