| The mechanisms by which nutrition and metabolic state affect fertility in cyclic gilts were studied. Experiment 1 tested the impact of different patterns of feed restriction between d 1 and 15 of the estrous cycle on subsequent fertility. HH gilts were fed 2.8 X maintenance throughout the cycle, in contrast to restriction (2.1 X maintenance) in the first (RH) or the second (HR) week of the cycle. Embryonic survival was reduced (P < .05) in HR gilts, without affecting ovulation rate. HR gilts also had lower (P < .05) plasma progesterone concentrations at 48 and 72 h after onset of estrus compared to HH and RH gilts.; In Experiment 2, RH and HR gilts were bred by AI and fertilization was allowed to occur in vivo; early fertilized oocytes were then recovered for culture in vitro, to assess the effect of the patterns of feed restriction on embryonic development. There was no effect of treatment on embryo developmental competence, however fertilization rate was lower (P < .06) in HR compared to RH gilts. Ovulation rate was again not different in the RH and HR treatments, but no differences in plasma progesterone were observed.; In Experiment 3, the responses to insulin treatment during the period of feed restriction in the late luteal phase that had deleterious effects on subsequent fertility were investigated. Feed restriction did not affect plasma insulin, IGF-I, leptin, total and freeT3, nor plasma LH, FSH, estradiol and progesterone on days 15 and 16 of the treatment cycle. In the subsequent peri-estrus period, plasma concentrations of LH, FSH, estradiol and progesterone were higher (P < .05) in RH and HR+I compared to HR gilts. There was again no treatment effect on embryo development.; These results demonstrate that feed restriction during the later part of the estrous cycle had lasting effects on ovarian function and endocrine status in the peri-estrus period, which may mediate differences in embryonic survival to day 28, apparently irrespective of effects of treatment on the developmental competence of fertilized oocytes. |
