Follicular Development and Function of Induced Corpora Lutea in Underfed Postpartum Anestrous Beef Cows

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Abstract
Effects of energy restriction during late gestation and early lactation on pituitary and ovarian responses to FSH and GnRH, and the effects of exogenous FSH or estradiol on follicular growth and luteal function after GnRH were examined in three experiments. In experiment I, 43 2-year-old Hereford heifers were assigned randomly 30 days prior to expected calving to be fed either 115% or 60% of the NRC recommended energy requirements. Although cows on the low plane lost more weight (P<.01) through the first 30 days after parturition, level of feeding had no effect on size of the largest ovarian follicle or concentration of plasma estradiol-17)β at 30 days postpartum. At 30 days postpartum cows received injections twice daily of 0,. 125 or .25 mg FSH for 3 days and were then treated with 300 μg GnRH. Dose of FSH did not affect estradiol-17β in daily plasma samples. Concentrations of LH in jugular blood samples taken every 30 min for 7 hr after GnRH were affected by plane of nutrition (P<.01). There was a positive association between follicle size and both the pattern of release of LH (P<.01) and the area under the LH response curve (P<.05). Occurrence of CL after GnRH was not related to body weight postpartum, change in weight during lactation, amount of LH released, follicle size, nutrition or dose of FSH. In 22 of 23 cows the CL palpated on day 7 had regressed by day 14 and progesterone in plasma at 3- or 4-day intervals after GnRH reflected a shortened life span of the induced CL. In experiment II, 17 cows that did not have CL in experiment I were injected twice daily for 3 days with either 0 or 2 mg FSH followed by injection 300 μg GnRH. Concentrations of estradiol-17β in plasma collected prior to FSH were correlated with body weights at 48 days postpartum (r = .70). Estradiol prior to GnRH, was correlated with size of the largest ovarian follicle (r = .53) at that time. Treatment with FSH (4 mg/day) increased mean diameter of the largest follicle (P<.05), but not estradiol-17β prior to GnRH. The proportion of cows that formed CL was not higher in cows pretreated with FSH (88%) than in controls (56%). Progesterone in plasma at 14 days after GnRH indicated that induced CL were short-lived. In experiment III, 18 3-year-old cows were treated twice daily from day 34 to 38 postpartum as follows: (1) corn oil for 1 day followed by saline for 3.5 days, (2) corn oil for 1 day plus increasing doses of FSH for 3.5 days or (3) estradiol benzoate (75 μg) for 1 day plus FSH for 3.5 days. GnRH (300 μg) was administered 4 days after initiation of treatments. FSH or estradiol plus FSH did not affect follicular development, profiles of estrogen or LH, or occurrence or lifespan of induced CL. Sixty-one percent of the cows had CL on day 7 and progesterone in plasma of those cows averaged only 1.4 ng/ ml on day 7 and 45% of these CL were short-lived. Copyright © 1979. American Society of Animal Science . Copyright 1979 by American Society of Animal Science.