title: Hourly administration of GnRH to prepubertal gilts: endocrine and ovulatory responses from 70 to 190 days of age.
abstract: This study investigated the responsiveness of the pituitary-ovarian axis of prepubertal gilts to hourly injections (i.v.) with GnRH. Six gilts each at 70, 100, 150, and 190 d of age were assigned either to treatment with GnRH or saline. Treatments were given until gilts showed estrus or for 7 d, whichever came first. Hourly pulsing with GnRH resulted in gradually increasing concentrations of estradiol-17 beta (E2), a preovulatory surge of LH, and subsequently increased progesterone (P4) concentrations. The increase in serum P4 was preceded by ovulation and corpora lutea (CL) formation in two gilts 70 d of age and all older gilts. The interval (h) from start of GnRH treatment to peak E2 (88 +/- 3), peak LH (103 +/- 3), and concentrations of P4 greater than or equal to 1 ng/mL (144 +/- 4) did not differ (P greater than .50) for 18 gilts between 100 and 190 d of age. In two ovulating, 70-d-old gilts, the interval from onset of GnRH treatment to peak E2 (171 +/- 6), peak LH (186 +/- 0), and P4 greater than or equal to 1 ng/mL (216 +/- 4) was lengthened (P less than .001). Peak concentrations of E2 (pg/mL) were higher (P less than .01) at 190 d (48 +/- 2) and 150 d (49 +/- 2) than at younger ages and lower (P less than .01) in gilts 70 d of age (31 +/- 1) than in gilts 100 d of age (41 +/- 2). Peak LH (nanograms/milliliter) was higher (P less than .01) in gilts 100 d of age (12.7 +/- 6) than in older gilts. Concentrations of P4 were similar (P greater than .20) for all ovulating gilts. The number of CL (12.7 +/- .7) did not differ (P greater than .20) for 18 gilts 100 d of age or older but was higher (P less than .01) than that (4.5 +/- 1.1) for two gilts 70 d of age. Corresponding endocrine responses or ovulations were not observed in four 70-d-old gilts treated with GnRH or in gilts given saline. These findings indicate that the functional integration of the pituitary-ovarian axis is completed between 70 and 100 d of age. Hourly treatment with GnRH is an adequate stimulus to induce ovulation in prepubertal gilts as early as 70 d of age. Also, the number of follicles reaching ovulatory competency was similar (P greater than .20) in gilts between 100 and 190 d of age, when GnRH was given on a BW basis.
authors.affiliation: College of Veterinary Medicine, North Carolina State University, Raleigh 27606.
authors.forename: A
authors.initials: A
authors.lastname: Pressing
authors.forename: G D
authors.initials: GD
authors.lastname: Dial
authors.forename: K L
authors.initials: KL
authors.lastname: Esbenshade
authors.forename: C M
authors.initials: CM
authors.lastname: Stroud
mesh_terms: D000375:Aging / Q000502:physiology*; D000818:Animals; D004958:Estradiol / Q000097:blood; D004971:Estrus / Q000187:drug effects; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000008:administration & dosage / Q000494:pharmacology*; D006728:Hormones / Q000097:blood*; D007986:Luteinizing Hormone / Q000097:blood; D010060:Ovulation / Q000187:drug effects*; D011374:Progesterone / Q000097:blood; D012741:Sexual Maturation; D013552:Swine / Q000502:physiology*
chemical_list: D006728:Hormones; D007987:Gonadotropin-Releasing Hormone; D011374:Progesterone; D004958:Estradiol; D007986:Luteinizing Hormone