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Changes in Plasma Hormone Concentrations Associated with the Onset of Puberty in the Gilt^1,2,

University of Missouri⁵, Columbia 65211

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-17β (E₂β) concentrations increased from d —6 to a peak on d —2 of 20 pg/ml (d 0 = day 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 E₂β 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 E₂β 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 d - 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.

¹ Contribution from the Missouri Agr. Exp. St a. Journal Ser. No. 8762.

² This investigation was supported in part by Grant Number CSRS 701-15-44 from the USDA. The authors express appreciation to Lei Yen for technical assistance and to Darlene Bender and Betty Nichols for secretarial assistance.

³ Present address: Dept. of Anim. Sci., North Carolina State Univ., Raleigh, NC 27650.

⁴ Present address: School of Agriculture, Univ. of Nottingham, Sutton Bonington, Loughborough LEI2 5RD, United Kingdom.

⁵ Dept. of Anim. Sci.