دورية
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 estrogen1
| العنوان: | 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 estrogen1 |
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| المؤلفون: | Sesti, Luiz A. C., Britt, Jack H. |
| المصدر: | Journal of Animal Science; April 1993, Vol. 71 Issue: 4 p989-998, 10p |
| مستخلص: | 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 µg/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-170 (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 (10µg/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. All sows showed estrus within 72 h after EB, but at mid-lactation, more sows whose litters had been weaned 4 d earlier had LH surges than sows whose litters were weaned at EB treatment (3 of 4, 2.2 ± .37 ng/mL vs 1 of 4, 1.58 ± .28). At late lactation there was no difference in the proportion of sows that had LH surges (3 of 4, 2.53 ± .74 vs 3 of 4, 2.93 ± 1). These results indicate that 1) estrus induced by EB occurs similarly at mid- and late lactation, 2) a smaller number of surges of LH occurs at mid- than late lactation, apparently because of inadequate releasable pools of pituitary LH, and 3) suckling prevents ovulation following a LH surge induced by EB in lactating sows. |
| قاعدة البيانات: | Supplemental Index |
| تدمد: | 00218812 15253163 |
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| DOI: | 10.2527/1993.714989x |