Hormonal combinations for fixed-time artificial insemination aiming to optimize fertility outcomes of Nelore cattle

• Autor(a) principal: Alves, Rodrigo Lemos Olivieri Rodrigues
• Data de Publicação: 2020
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Biblioteca Digital de Teses e Dissertações da USP
• Texto Completo: https://www.teses.usp.br/teses/disponiveis/11/11139/tde-06102020-093054/
• topic: Expressão de estro; Expression of estrus; Fertilidade; Fertility; IATF; IATF; Ovulação; Ovulation; PGF; PGF; Protocol; Protocolo

Two studies were performed aiming to evaluate reproductive outcomes, including ovarian dynamics and fertility, of Nelore heifers and cows submitted to estradiol (E2)/progesterone (P4)-based fixed-time artificial insemination (FTAI) protocols. The first study was performed using suckled Nelore cows and evaluated some adjustments in protocols with 7 days of P4 implant duration. Cows received an intravaginal P4 implant on Day 0, associated with E2 benzoate (EB) administration, and the implant remained for 7 days. At the time of P4 implant removal, all cows were treated with equine chorionic gonadotropin (eCG), E2 cypionate (EC) and prostaglandin F2&#945; (PGF), and were inseminated 48 hours later. The first adjustment was made at the beginning of the protocol (Day 0) with or without PGF; the second adjustment was made at the time of P4 implant withdrawal (Day 7) and consisted of treating with either 0.5 or 1.0 mg EC. The third adjustment was administration or not of GnRH at the time of FTAI (Day 9). Regarding ovarian dynamics, multiparous had larger follicules than primiparous cows, on both Day 7 and at FTAI, in addition to a greater number of cows with CL at the initiation of the protocol. Overall, pregnancy per AI (P/AI) was high (&#8764;58%) and was not affected by PGF treatment on Day 0. Expression of estrus was higher in cows that received 1.0 mg EC, in addition to a tendency of greater P/AI. P/AI was greater when cows received GnRH at FTAI, particularly in cows not expressing estrus. Thus, GnRH improved P/AI especially in cows with lower expression of estrus, such as primiparous, thinner cows (BCS < 3.0), and cows treated with 0.5 mg of EC on Day 7. The second study evaluated the reproductive outcomes of Nelore heifers submitted to 7 or 9 d E2/P4-based FTAI protocols, with PGF administered at different times. An ultrasound evaluation was performed prior to the start of the experiment, to evaluate cyclicity. Heifers with CL were assigned to one of four experimental treatments, one with 7 days of P4 device, and PGF administered on Days 0 and 7, and the other with 9 days of P4 device, and PGF given at different times (Day 0 and 9, Day 7, or Day 9). Pre- pubertal heifers were submitted to a protocol for induction of cyclicity and, then, were randomly assigned to one of the four treatments, regardless of CL presence. Low number of heifers had CL at the first ultrasound evaluation (&#8764;17%), however, protocol for induction of cyclicity resulted in more than 80% of heifers with CL at the initiation of the synchronization protocol. The presence of CL on Day 0, overall, was positively affected by body condition score, although it did not influence expression of estrus and P/AI. There were differences on ovarian dynamics, with lower follicular diameter, at the time of AI, on animals from group 7 d. Expression of estrus was high (&#8764;90%) and did not affect P/AI, which also was similar between groups (&#8764;53%). Therefore, the studies evaluated strategies using FTAI protocols, either for Nelore heifers or cows, allowing for flexibility in the use of protocols and in schedules for FTAI programs.