The effect of acute nutritional change on follicle wave turnover, gonadotropin, and steroid concentration in beef heifers

The effects of acute nutritional change on endocrine and ovarian characteri stics were studied in cyclic (intact; n = 20) and long-term ovariectomized (ovx; n = 18) heifers being fed 1.2 x maintenance (1.2M). On d 7 of an 8-d progesterone and estradiol treatment, intact and ovx heifers were randomly allocated to diets providing .4, 1.2, or 2.0M until emergence of the second follicular wave after ovulation in intact heifers. In intact heifers, two of eight fed .4M failed to ovulate. In the other six, growth rate and maxim um diameter (1.1 +/- .09 mm/d and 10.1 +/- .7 mm, respectively) of the firs t dominant follicle (DF) postovulation were less (P < .05) than in heifers fed either 1.2 (1.6 +/- .18 mm/d; 12.9 +/- .44 mm) or 2.0M (1.6 +/- .08 mm/ d; 12.7 +/- .7 mm). In intact heifers, LH pulse frequency and amplitude wer e not affected by diet (P > .10). In ovx heifers, the frequency of LH pulse s was unaffected by diet (P > .10), but heifers fed .4M had a greater pulse amplitude (P < .05) and mean concentration of LH (P < .001) than those fed 1.2 or 2.0M. Plasma concentrations of FSH were greater (P < .05) in ovx he ifers fed .4M than in those fed 1.2 or 2.0M and increased linearly with tim e (P < .01). The FSH concentrations in heifers fed 1.2 and 2.0M were simila r (P > .10) and decreased linearly with time (P < .001). In intact heifers, concentrations of FSH preceding follicle wave emergence were greater in he ifers fed .4M (P < .001), but basal concentrations were not affected (P > . 10). Concentrations of progesterone and estradiol were unaffected by diet ( P > .10). Significant diet x ovarian status interactions in plasma IGF-I co ncentrations existed. Plasma concentrations of insulin increased as the lev el of nutrition increased, whereas concentrations of NEFA decreased. In con clusion, growth rate and maximum diameter of the DF were decreased by acute nutritional restriction, without affecting the concentration of LH. The ma gnitude of the FSH increase preceding new follicle wave emergence increased following dietary restriction, but concentrations of FSH were unaffected d uring the other stages of DF growth. The results of this study may have imp ortant implications for the feeding strategies adapted for high-yielding da iry cows in the early postpartum period when feed intake is often physiolog ically restricted.