Perinatal nutritional effects on postpubertal secretion of gonadotropins and feedback responsiveness to estradiol-17β in sexually mature heifers

Abstract

Developmental changes in response to nutritional extremes may in some cases be manifested later in adult life. Objectives of experiments reported herein were to test the hypotheses that maternal nutrition during mid- to late-gestation interacts with postnatal nutrition during the juvenile period in heifers to impact 1) tonic secretion of gonadotropins, and 2) estradiol-17β (E2) negative and positive feedback responsiveness in adulthood. Heifers were selected from a larger population programmed nutritionally using a 3 × 2 factorial arrangement of pre- and postnatal diets. Beginning at 90 days of pregnancy, Bos indicus-influenced cows (n = 95) bearing heifer fetuses were fed to achieve body condition scores (BCS; 1-9 scale) of 3-3.5 (L; thin), 5.5-6 (M; moderate), or 7.5-8 (H; obese) by onset of the third trimester and maintained thereafter. Heifer offspring were weaned at 3-3.5 mo of age and assigned to either a low- (L; 0.5 kg/d) or high-gain (H; 1.0 kg/d) diet until 8 mo of age, then fed a common diet until puberty. Heifers (n = 18; 6/group) representing HH, MH, and LL combinations were ovariectomized postpubertally and received E2 replacement. In Exp. 1, blood samples were collected at 10-min intervals to evaluate pulsatile secretion of luteinizing hormone (LH) and follicle stimulating hormone (FSH) for 5.5 h. Heifers in the MH group (1.25 ± 0.11 ng/mL) tended (P < 0.09) to have greater amplitude of LH pulses compared to HH (0.91 ± 0.14 ng/mL) and LL groups (0.96 ± 0.09 ng/mL); otherwise, frequency, amplitude, and mean concentrations of LH and FSH did not differ among groups. In Exp. 2, heifers received E2 (2.4 ug/kg I.M.), with blood sampling at 30-min to 1-h intervals for 30 h. Exogenous E2 (Exp. 2) suppressed (P < 0.0001) mean plasma concentrations of LH and FSH equally among groups, then stimulated equivalent surges of LH beginning at 14 ± 0.4 h, with only two FSH surges detected. Similarly, neither negative nor positive feedback responsiveness to E2 differed among the treatment combinations studied..