The effects of acute nutritional restriction on LH and oestradiol concentrations, follicle dynamics and fertility in heifers

Abstract

AbstractThe effects of acute nutritional change on endocrine and ovarian parameters were studied in two experiments. In both experiments, cyclic beef heifers fed a diet of 1.2 times maintenance (1.2 M) were synchronised using an intravaginal progesterone releasing device which was removed after 8 days. In Experiment 1, heifers were randomly allocated to a diet of either 0.4, 1.2 or 2.0 M one day before progesterone withdrawal. The dominant follicle present at progesterone withdrawal (synchronised DF) failed to ovulate in 2/8 heifers fed 0.4 M, and both growth rate (P<0.05) and maximum diameter (P<0.05) of the first new follicular wave was less than in heifers fed either 1.2 or 2.0 M. There was no effect of diet on LH pulse characteristics at emergence, selection or dominance phases of the first follicle wave of the next cycle (P>0.10). Due to anovulation of the synchronised DF in Experiment 1, a further experiment was conducted (Experiment 2) to examine pro-oestrus oestradiol and LH concentrations at both ovulation of the synchronised DF and prostaglandin-induced ovulation of the first DF of the next cycle (when insemination was performed). All heifers had a pro-oestrus increase in the concentration of oestradiol following progesterone withdrawal, but 2 heifers fed 0.4 M did not have an LH surge and did not ovulate. The first DF after the synchronised DF failed to ovulate in 12/20 heifers fed 0.4 M (P<0.05), always preceded by absence of a pro-oestrus increase in oestradiol and an LH surge. Where heifers ovulated, there was no effect of diet on conception rate. We conclude that acute nutritional restriction of beef heifers caused an immediate suppression in the growth rate and maximum diameter of dominant follicles, but this occurred without any suppression effect on LH pulse characteristics. Restriction to 0.4 M induced anovulation in 60% of heifers within 14 days and this was preceded by the absence of an LH surge. Where ovulation did occur, acute NEB in the final stages of follicle maturation did not appear to affect pregnancy rate.