title: Acute follicular response to FSH in heifers downregulated long term with a GnRH agonist and with suppressed ovarian follicular growth.
abstract: The objectives of this study were to (1) ascertain ovarian follicular status in heifers where the pituitary gonadotrope cells producing LH and FSH were downregulated by long-term treatment with a GnRH agonist and (2) characterize the acute superstimulation of follicular growth in response to FSH in heifers where the pituitary was downregulated with a GnRH agonist. At the start of the study, heifers (3 year old) were implanted with GnRH agonist (n = 20) or received no treatment (control, n = 5). After 6 months, follicular growth in heifers implanted with GnRH agonist was restricted to early antral follicles (2-4 mm). At this time, these heifers were allocated to four groups and follicular development was superstimulated with FSH as follows: group 1 (n = 5) and group 2 (n = 5), a conventional FSH protocol with injections over 4 days (Days 0-3) with Group 2 receiving two times the normal dose of FSH; group 3 (n = 5), a single injection of FSH in saline on Day 0; group 4 (n = 5), a single injection of FSH in slow-release polyvinylpyrrolidone on Day 0. Follicular growth in the control heifers (n = 5) was superstimulated using the conventional 4-day FSH protocol. On Day 5, heifers in groups 1 and 2 had similar (P > 0.05) numbers of follicles in the size categories 6 to 7 mm (12.8 ± 3.0 follicles) and 8 to 9 mm (6.5 ± 1.0) as control heifers (6-7 mm, 14.6 ± 2.2; 8-9 mm, 6.2 ± 2.2) and six of the former heifers had follicles 10 mm (3.2 ± 1.4). Also on Day 5, follicular growth for heifers in group 3 was restricted to 4 to 5 mm (11.6 ± 3.0) and 6 to 7 mm (7.6 ± 3.7), whereas four out of five heifers in group 4 had follicles of 6 to 7 mm (8.2 ± 2.3) and three heifers had follicles of 8 to 9 mm (4.6 ± 2.2) and 10 mm (2.2 ± 0.9). Injection of exogenous LH on Day 5 induced ovulation in 9 out of 10 heifers in groups 1 and 2, no heifers in group 3, and 2 of 5 heifers in group 4. Plasma concentrations of progesterone 6 days after ovulation were the same (P > 0.05) for heifers in groups 1 and 2 (8.9 ± 0.9 ng/mL) and control heifers (10.0 ± 0.9 ng/mL). This study has shown that heifers treated chronically with a GnRH agonist have suppressed ovarian follicular growth but are able to respond to acute superstimulation with FSH. Furthermore, follicles in heifers treated with a GnRH agonist undergo morphologically normal growth in response to FSH and can ovulate and develop into a CL. The long-term GnRH agonist-treated heifer provides a practical model for repeated ovarian follicular superstimulation, multiple ovulation, and embryo transfer, without the need to control stage of the estrous cycle.
authors.affiliation: School of Agriculture and Food Sciences, The University of Queensland, Gatton Campus, Gatton, Queensland, Australia. Electronic address: m.docchio@uq.edu.au.
authors.forename: M J
authors.initials: MJ
authors.lastname: D'Occhio
authors.forename: F
authors.initials: F
authors.lastname: Cremonesi
authors.forename: T E
authors.initials: TE
authors.lastname: Trigg
authors.forename: W J
authors.initials: WJ
authors.lastname: Aspden
authors.forename: P S
authors.initials: PS
authors.lastname: Baruselli
mesh_terms: D000818:Animals; D002417:Cattle / Q000502:physiology*; D015536:Down-Regulation; D030762:Estrous Cycle; D005260:Female; D005640:Follicle Stimulating Hormone / Q000494:pharmacology*; D007987:Gonadotropin-Releasing Hormone / Q000819:agonists*; D007986:Luteinizing Hormone / Q000097:blood; D006080:Ovarian Follicle / Q000000981:diagnostic imaging / Q000187:drug effects* / Q000254:growth & development; D010060:Ovulation / Q000187:drug effects; D010062:Ovulation Induction / Q000662:veterinary; D011374:Progesterone / Q000097:blood; D014463:Ultrasonography
chemical_list: D007987:Gonadotropin-Releasing Hormone; D011374:Progesterone; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone
keywords: FSH; Follicular superstimulation; GnRH agonist; Heifer; Ovulation; Suppressed ovaries