Serum Profiles of Progesterone, LH, FSH and Prolactin Immediately Preceding Induced Puberty in Gilts2

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Abstract
Two experiments were conducted to determine if the secretory patterns of luteinizing hormone (LH), follicle stimulating hormone (FSH) and prolactin (PRL) and serum concentrations of progesterone change immediately preceding induced puberty in gilts. To help predict when prepubertal gilts would attain puberty, gilts were induced into puberty by relocation from confinement housing to an outdoor lot and exposure to mature boars. In Exp. 1, 17 prepubertal gilts were bled on two successive days from 0800 to 1200 h before relocation and boar exposure and until the second day of estrus or for 8 d in gilts that failed to exhibit estrus. Blood samples were collected from indwelling cannulas at 20-min intervals for 4 h. In Exp. 2, blood samples were collected from 20 prepubertal gilts at 20-min intervals from 0800 to 1200 h and from 2000 to Z400 h until the second day of estrus or for 6 d if the gilt failed to exhibit estrus. In each experiment, 11 gilts exhibited pubertal estrus 3 to 6 d after relocation and boar exposure. When the frequency of LH spikes in each gilt was normalized to the day of her preovulatory surge of LH (d 0), a decline in the frequency of LH secretory spikes was observed as gilts approached puberty. However, neither the average magnitude of LH spikes nor mean LH concentrations were different among these days. Mean serum concentrations, frequency of spikes or average magnitude of secretory spikes of FSH or PRL did not change on the days preceding the preovulatory peak of LH. In Exp. 1, 8 of 11 gilts that exhibited estrus had higher (P<.05) serum concentrations of progesterone on d −1 and 0 than on d −3 and −2. In Exp. 2, 7 of 11 gilts that achieved estrus had greater (P<.05) serum concentrations of progesterone on d −.5 than on d −1.5, −1.0 and 0. No increases in serum progesterone were observed in the gilts that failed to exhibit estrus in either experiment. In both experiments, serum concentrations of estradiol-17β were elevated as gilts approached puberty. Serum concentrations of Cortisol remained unchanged on the days immediately preceding the preovulatory surge of LH. These results indicate that the frequency of LH secretory spikes decreased in gilts immediately preceding puberty induced by relocation and boar exposure. Of the 22 gilts that attained puberty, only 15 had a prepubertal rise of serum progesterone. Thus, it appears that a preovulatory rise in serum progesterone is not a necessary event for estrus or ovulation to occur in gilts. Copyright © 1984. American Society of Animal Science . Copyright 1984 by American Society of Animal Science.