GnRH34 with or without estradiol cypionate in timed AI in Bos indicus beef cows.

• Autor(a) principal: SILVA, S. A.
• Data de Publicação: 2023
• Outros Autores: MONDADORI, R. G., NOLETO, G. S., BARBOSA, I. P., GONÇALVES, R. L., GASPERIN, B. G., ROVANI, M. T., PAZ, E. F., GOMES, L. S., PFEIFER, L. F. M.
• Tipo de documento: Artigo
• Idioma: eng
• Título da fonte: Repositório Institucional da EMBRAPA (Repository Open Access to Scientific Information from EMBRAPA - Alice)
• Texto Completo: http://www.alice.cnptia.embrapa.br/alice/handle/doc/1154705; https://doi.org/10.1016/j.theriogenology.2023.06.026
• topic: Embrapa Rondôna; Amazônia Ocidental; Western Amazon; Reprodução Animal; Fertilidade Animal; Hormônio; Estradiol; Gado Nelore; Vaca de Corte; Bos Indicus; Prenhez; Ovulação; Campo Experimental; Animal reproduction; Animal fertility; Nellore; Beef cows; Hormones; Pregnancy; Ovulation; Demonstration farms

Two experiments were performed to evaluate the effects of GnRH treatment on the fertility of suckled Nelore beef cows treated with an estradiol/progesterone (E2/P4)-based protocol for timed artificial insemination (TAI). Experiment 1 focused on determining the effects of estradiol cypionate (EC) on ovulation in TAI cows treated with GnRH 34 h after removal of the intravaginal P4 device (IPD). Suckled cows (n ¼ 26) were treated with 2 mg estradiol benzoate (EB) and IPD containing 1 g P4. After 8 days, IPDs were removed, and all cows were treated with 150 mg of d-cloprostenol (prostaglandin F2 alpha analog) and 300 IU of equine chorionic gonadotropin (eCG), then separated into two treatment groups consisting of cows who received 1) saline 0.9% i.m. (GnRH34 group) or 2) 0.6 mg i.m. of EC (EC-GnRH34 group). On day 9 (05:00 p.m.), all cows were given GnRH (10.5 mg of buserelin acetate) i.m. No differences were observed between the groups (P > 0.05) in the time of ovulation after IPD removal or in the proportion of cows ovulating. Experiment 2 focused on determining the effects of GnRH34 along with or in the absence of EC on day 8 on pregnancy per AI (P/AI) in postpartum beef cows. Cows (n ¼ 981) were treated similarly to those in Experiment 1, but an additional group, the EC-GnRH48 group, was included, in which cows received EC on day 8 whereas those that did not show estrus received GnRH at TAI. Thus, in this experiment, groups consisted of GnRH34 (n ¼ 322), EC-GnRH34 (n ¼ 335), and EC-GnRH48 (n ¼ 324). A higher rate of estrus expression was observed in cows treated with EC following IPD removal (EC-GnRH34: 69%, EC-GnRH48: 64.8%) than in cows in the GnRH34 group (45.6%). No difference in P/AI was observed between the treatment groups (P ¼ 0.45), but P/AI in cows in the EC-GnRH34 group (64.2%) tended to be greater (P ¼ 0.1) than in cows in the GnRH34 group (58%). In summary, although ovulation synchrony did not differ among the groups, P/AI in cows treated with EC and GnRH 34 h after IPD removal tended to be greater than in cows treated solely with GnRH; this was most likely due to a shorter proestrus/estrus period, considering the lower proportion of cows that displayed estrus in the GnRH34 group. Finally, given that P/AI did not differ between the EC-GnRH34 and EC-GnRH48 groups, our results suggest that, for cows not displaying estrus, administration of EC at the time of IPD removal followed by treatment with GnRH 48 h afterward represents the most cost-efficient TAI strategy for South American Zebu-based beef operations.