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

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)

Endocrine bases of lactational anoestrus in the sow

“…Between the third and fourth week of lactation, there is a partial recovery of the positive feedback response to OB (Cox et al, 1988;Elsaesser et al, 1992;Sesti and Britt, 1993). However, even with a massive dose of OB (60 pg/kg body weight), the amplitude of the LH peak remains much lower than that observed in cyclic or OB-treated prepubertal females (Elsaesser and Parvizi, 1980).…”

“…The number of large follicles increases during the first 2 months of pregnancy and declines thereafter, whereas the number of small follicles tends to increase (Rexroad and Casida, 1975 (Elliot et al, 1980) and a high incidence of cystic follicles (Peters et al, 1969 (Ryan and Raeside, 1991). A dysfunction in the oestrogen-induced positive feedback in lactating sows shortly after farrowing (until 14-16 6 days pp) has also been described (Elsaesser and Parvizi, 1980;Cox et al, 1988;Sesti and Britt, 1993 Uterine involution could also play a role in the long-term effects of pregnancy. In lactating sows, uterine involution is achieved within 21-28 d pp (Palmer et al, 1965a,b (Baldwin and Plucinski, 1977 (Salmon Legagneur, 1956;Jensen and Recén, 1989).…”

Agonist-Induced Release of Gonadotropin-Releasing Hormone, Luteinizing Hormone, and Follicle-Stimulating Hormone and their Associations with Basal Secretion of Luteinizing Hormone and Follicle-Stimulating Hormone throughout Lactation in Sows

“…Pituitary concentrations of LH and FSH have been reported to be lower in early than in late lactation [1][2][3][4][5]. The greater secretion of gonadotropins in late lactation is accompanied by an increase in number of larger follicles (> 6 mm) and greater serum concentrations of estrogens [1,6,7].…”

Influence of Cumulative Feed Intake during Early and Mid-Lactation on Luteinizing Hormone Secretion and Weaning-to-Estrus Interval in Primiparous Sows.

“…We could not detect the treatment difference in mean LH concentrations. This is probably because LH release during mid-lactation (12 days) is low (0.3 to 0.5 ng/ml) [16], and it is close to our assay sensitivity, 0.30 ng/ml.…”