title: Ovarian follicular growth suppression by long-term treatment with a GnRH agonist and impact on small follicle number, oocyte yield, and in vitro embryo production in Zebu beef cows.
abstract: The aim of the present study was to evaluate small follicle number, oocyte yield, and in vitro embryo production (IVEP) in Zebu beef cows treated long term with a GnRH agonist to suppress ovarian follicular growth. Nelore (Bos indicus) cows (n = 20) showing regular estrous cycles were randomly assigned to one of two groups: control (n = 10, placebo ear implant without a GnRH agonist); GnRH agonist (n = 10, GnRH agonist ear implant containing 9.4-mg deslorelin). All cows underwent an ovum pick-up (OPU) session 14 days (Day 14) before the start of treatments (Day 0) followed by seven OPU-IVEP procedures at 30-day intervals (Days 0, 30, 60, 90, 120, 150, and 180). Semen from a single batch of a previously tested bull was used for all the IVEP. Cows treated with agonist reported a decrease over time in the proportion of animals with a (CL; P ≤ 0.05) and large follicles (>10 mm, P ≤ 0.05). These cows had a lesser number of medium + large follicles (>5 mm; 1.74 ± 0.5 vs. 4.13 ± 0.5; P ≤ 0.05), greater number of small follicles (2-5 mm; 44.3 ± 2.8 vs. 30.8 ± 1.8; P ≤ 0.05), greater yield of cumulus-oocyte complexes (COCs; 21.0 ± 2.3 vs. 15.6 ± 1.9; P ≤ 0.05), greater proportion of COCs cultured (79.2 vs. 73.9%; P ≤ 0.05), COCs cleaved (10.6 ± 1.5 vs. 6.8 ± 1.1, P ≤ 0.05), and cleaved rate (52.8 vs. 44.3%; P ≤ 0.05) compared with control cows. The number (3.4 ± 0.7 vs. 3.0 ± 0.6; P > 0.05) and proportion (16.5 vs. 19.1%; P > 0.05) of blastocysts produced were similar between agonist and control cows, respectively. The study has shown that Zebu beef cows treated long term with a GnRH agonist had follicular growth restricted to small follicles. This did not compromise the ability of oocytes to undergo IVF and embryonic development.
authors.affiliation: Department of Animal Reproduction, University of São Paulo, São Paulo, SP, Brazil.
authors.forename: E O S
authors.initials: EOS
authors.lastname: Batista
authors.affiliation: Department of Animal Reproduction, University of São Paulo, São Paulo, SP, Brazil.
authors.forename: L M
authors.initials: LM
authors.lastname: Vieira
authors.affiliation: Department of Animal Reproduction, University of São Paulo, São Paulo, SP, Brazil.
authors.forename: M F
authors.initials: MF
authors.lastname: Sá Filho
authors.affiliation: Instituto de Zootecnia, Centro APTA Bovinos de Corte, Sertãozinho, SP, Brazil.
authors.forename: E A R
authors.initials: EAR
authors.lastname: Dias
authors.affiliation: Department of Animal Reproduction, University of São Paulo, São Paulo, SP, Brazil.
authors.forename: B M
authors.initials: BM
authors.lastname: Bayeux
authors.affiliation: Sexing Technologies, Sertãozinho, SP, Brazil.
authors.forename: M F
authors.initials: MF
authors.lastname: Accorsi
authors.affiliation: Instituto de Zootecnia, Centro APTA Bovinos de Corte, Sertãozinho, SP, Brazil.
authors.forename: F M
authors.initials: FM
authors.lastname: Monteiro
authors.affiliation: Ceva Santé Animale, Libourne, Gironde, France.
authors.forename: A H
authors.initials: AH
authors.lastname: Souza
authors.affiliation: Department of Animal Reproduction, University of São Paulo, São Paulo, SP, Brazil. Electronic address: barusell@usp.br.
authors.forename: P S
authors.initials: PS
authors.lastname: Baruselli
authors.affiliation: Faculty of Agriculture and Environment, The University of Sydney, Sydney, New South Wales, Australia.
authors.forename: M J
authors.initials: MJ
authors.lastname: D'Occhio
mesh_terms: D000818:Animals; D002417:Cattle; D004622:Embryo, Mammalian / Q000187:drug effects; D047108:Embryonic Development / Q000187:drug effects; D005260:Female; D005307:Fertilization in Vitro / Q000662:veterinary; D007987:Gonadotropin-Releasing Hormone / Q000819:agonists* / Q000494:pharmacology; D009865:Oocytes / Q000187:drug effects; D006080:Ovarian Follicle / Q000187:drug effects*
chemical_list: D007987:Gonadotropin-Releasing Hormone
keywords: Bovine; Follicle; GnRH agonist; IVF; Oocyte; Zebu