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  • Title: Influence of stage of lactation, exogenous luteinizing hormone-releasing hormone, and suckling on estrus, positive feedback of luteinizing hormone, and ovulation in sows treated with estrogen.
    Author: Sesti LA, Britt JH.
    Journal: J Anim Sci; 1993 Apr; 71(4):989-98. PubMed ID: 8478298.
    Abstract:
    The overall objective of this study was to investigate the LH response and occurrence of estrus and ovulation in sows treated with estradiol benzoate (EB) at mid- (d 14) or late (d 28) lactation. Experiment 1 tested the hypothesis that hourly pulses of LHRH given to sows treated with EB would cause a greater proportion to exhibit LH surges. Sows (n = 32) at mid- or late lactation were given (i.m.) corn oil (CO) or EB (10 micrograms/kg BW) at 0 h and no pulses or hourly pulses (100 ng/pulse) of the LHRH agonist des-Gly10,[D-ALA6]-LHRH ethylamide (LHRH-A) from 54 to 96 h, the anticipated period of positive feedback of LH. Blood samples for determination of estradiol-17 beta (E2) and LH were collected every 6 h from -12 to 120 h from sows treated with EB. Estrus was checked daily with a mature boar, and ovulation was assessed by measuring progesterone in blood 1 wk after estrus induced by EB or 2 wk after weaning at 34 +/- 1.4 d postpartum. Lactational estrus occurred in 0 of 16 and 15 of 16 sows given CO and EB, respectively; however, no sow ovulated in response to EB. Concentrations of LH were lower (P < .01) during mid- than during late lactation, and LHRH-A pulses had no effect on secretion of LH and E2. The LH concentrations during the pretreatment (-12 to 0 h), negative feedback (6 to 54 h), and positive feedback (60 to 96 h) periods at mid-lactation (.32 +/- .03, .22 +/- .01, and .54 +/- .08 ng/mL, respectively) differed (P < .01) from values at late lactation (.80 +/- .06, .49 +/- .02, and 1.47 +/- .17, respectively). Preovulatory-like surges of LH occurred in one of eight (peak 2.1 ng/mL) and seven of eight (peak 2.9 +/- 1 ng/mL) sows given EB at mid- and late lactation, respectively. Experiment 2 tested the hypothesis that the hypothalamus and pituitary of sows weaned 96 h before they were given EB would show a greater responsiveness than those weaned and given EB simultaneously. Sows (n = 16) at mid- or late lactation were treated with EB (10 micrograms/kg BW; i.m.), and one-half of the sows were suckled until the moment of EB treatment, whereas the other half had their litters weaned 96 h before treatment with EB.(ABSTRACT TRUNCATED AT 400 WORDS)
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