Changes in Plasma Hormone Concentrations Associated with the Onset of Puberty in the Gilt2

Abstract

Hormonal changes during the follicular phase of gilts exhibiting their first estrus were examined in response to either relocation and boar exposure or treatment with pregnant mare serum gonadotropin (PMSG). In the first experiment, blood was collected from nine gilts from 6 d before to 6 d after the onset of first estrus. Mean estradiol-17 beta (E2 beta) concentrations increased from d -6 to a peak on d -2 of 20 pg/ml (d 0 = of estrus) and then declined gradually over the next 6 d until basal levels (2.4 pg/ml) were reached. Mean concentrations of luteinizing hormone (LH) fluctuated between .5 to 1 ng/ml before d 1.5 and after d 1.5, with the ovulatory surge occurring on either d -1 or d 0 and averaging 6.2 ng/ml. Progesterone (P) concentrations were less than .3 ng/ml until formation of corpora lutea, while concentrations of glucocorticoids (CORT) ranged from 7.4 to 24.5 ng/ml. In Exp. 2, blood was collected every 6 h from d -2 to d 14 from eight gilts that were exposed to boars on d 0. Four of the gilts exhibited estrus and had a hormonal profile similar to that of gilts in Exp. 1. Concentrations of E2 beta were elevated in two gilts after exposure to a boar, but concentrations of LH were not altered. The remaining two gilts had basal concentrations of E2 beta and LH throughout the blood sampling period. In Exp. 3, blood was sampled from five gilts twice daily for 8 d following the administration of 1,000 IU PMSG. Estrus was exhibited by all gilts on the fifth day after PMSG. Circulating concentrations of total estrogens peaked on -1 while concentrations of LH peaked on d 0. Concentrations of P were low until after estrus and CORT levels displayed a diurnal pattern throughout. The results indicate that the hormonal profiles during the pubertal follicular phase of gilts induced by relocation and boar exposure or PMSG are similar. Furthermore, no changes were observed in P concentrations immediately before or during the pubertal follicular phase, suggesting that progesterone priming may not be prerequisite to puberty in gilts.

Differential effects of 17β-estradiol, conjugated equine estrogen, and raloxifene on mRNA expression, aggregation, and secretion in platelets

“…Circulating concentrations of 17␤-estradiol show a cyclic pattern in pigs (13), as would be expected for adult animals with an estrous cycle. In animals with ovaries, plasma estradiol varies from 21.6 Ϯ 3.1 pg/ml to levels below the detection limit of the assay (1).…”

Effect of short-term elevations in plasma cortisol concentration on LH secretion in prepubertal gilts

“…2 (1984) observed no significant effect of exogenous cortisol or ACTH on GnRH-induced secretion of LH in intact prepubertal gilts, they used a very large dose of 400 pg GnRH which may have over-ridden any changes in pituitary responsiveness. The dose of GnRH used in the present study induced an LH release within the normal physiological range for gilts reaching puberty (Esbenshade et al, 1982). The concentrations of plasma cortisol obtained as a result of the infusion were also within the range of levels reported for gilts approaching puberty (Diekman & Trout, 1984) although they were higher than levels observed in gilts exposed to boars (Pearce & Hughes, 1987).…”

Physiological mechanisms of ovarian follicular growth in pigs — A review

“…Probably this is the reason why the levels of this hormone remain relatively low despite the increase in ovarian follicular activity (Camous et al, 1985). A significant increase in serum oestradiol concentration was observed directly before the first ovulation and was associated with the first oestrous behaviour (Esbenshade et al, 1982).…”