Influence of nutrition on pre-partum plasma levels of progesterone and total oestrogens and post-partum plasma levels of luteinizing hormone and follicle stimulating hormone in suckling cows

Abstract

ABSTRACTTwo groups of suckling Charolais cows were fed at different levels of nutrition from 70 days before the estimated date of calving until 45 days after calving, to study the effects of reduced dietary intake on pre-partum plasma levels of progesterone and total oestrogens (conjugated + unconjugated) and post-partum plasma levels of luteinizing hormone and follicle stimulating hormone. Eight control cows received a ration containing the Institut National de la Recherche Agronomique's recommendations for all nutrients, while 10 cows received a restricted diet which supplied approximately three-quarters of the recommended amounts for energy and nitrogen.The mean weight of the two groups of cows was similar at the beginning of the experiment but the restricted group had a significantly lower weight just before calving than the control group (678 v. 766 kg; P < 0·05).After calving, cows ont he low diet had a weight loss of 600 g/day, while those on the control diet gained 300 g/day. During the last 45 days of pregnancy underfeeding did not significantly affect oestrogen levels, but progesterone levels increased proportionally by 0·24 (P < 0·01).During the first 45 days of lactation underfeeding decreased the number of cows showing oestrus (0/10 v. 4/8) and significantly decreased both luteinizing hormone and follicle stimulating hormone levels at 5, 15 and 30 days post partum.Furthermore, the correlation between mean daily gain (0 to 45 days post partum) and luteinizing hormone concentration on day 30 was highly significant (r = 0·58; P < 0·01; no. = 19). These results suggest that the delay of the first post-partum ovulation in the underfed cow is due to low gonadotropin levels.