Progesterone-based timed AI protocols for Bos indicus cattle III: Comparison of protocol lengths

Author(s):Show less -

Prata, Alexandre B. ^{[1, 2]} ; Madureira, Guilherme ^{[1, 3]} ; Robl, Adelino J. ^[4] ; Ribeiro, Heuller S. ^[4] ; Sagae, Milton ^[4] ; Elias, V, Manoel C. ; Pimenta, Cesar ^[5] ; Barrios, Jhonny ^[5] ; Hartmman, Diego ^[5] ; Schneider, Althuir A. ^[2] ; Sandoval, Gabriel A. F. ^[2] ; Wiltbank, Milo C. ^[3] ; Sartori, Roberto ^{[1, 3]}

Affiliation

^[1] Univ Sao Paulo, Luiz de Queiroz Coll Agr ESALQ, Dept Anim Sci, Av Padua Dias 11, BR-13418900 Piracicaba, SP - Brazil

^[2] GlobalGen Vet Sci, Av Italo Poli 40, BR-14887360 Jaboticabal, SP - Brazil

^[3] Univ Wisconsin, Dept Anim & Dairy Sci, 1675 Observ Dr, Madison, WI 53706 - USA

^[4] Agr Roncador, Av Rio Grande do Sul 387, BR-78643000 Querencia, MT - Brazil

^[5] Elias, Manoel C., V, Agr Roncador, Av Rio Grande do Sul 387, BR-78643000 Querencia, MT - Brazil

• Document type: Journal article
• Source: Theriogenology; v. 152, p. 29-35, AUG 2020.
• Web of Science Citations: 0

Abstract

This study aimed to validate a 7 d progesterone (P4)-based fixed-time AI (FTAI) protocol for Bos indicus cattle by comparing to 8 and 9 d-type protocols. The first study compared 7 vs. 8 d protocols in Nelore heifers (Exp. 1.1; n = 742) and cows (Exp. 1.2; n = 2488), and the second study compared 7 vs. 9 d protocols in cows (Exp. 2; n = 1343). On experimental Day -10 and Day -11 the 8 and 9 d groups received an intravaginal P4 implant, 2.0 mg estradiol benzoate (EB) and 0.5 mg cloprostenol sodium (PGF). On Day -9 the 7 d group received the same treatments (P4, EB, and PGF). Then, on Day -2 all groups had the P4 implants removed, and PGF, 0.6 mg estradiol cypionate, and 300 IU equine chorionic gonadotropin (eCG) was administered. Fixed-time AI was performed 48 h later (Day 0) and 8.4 mg buserelin acetate (GnRH) was administered to 7d-G, 8d-G and 9d-G groups, whereas 7d-0, 8d-0 and 9d0 groups did not receive GnRH at AI. Estrus was detected using tail-chalk between Day -2 and Day 0. Pregnancy per AI (P/AI) was evaluated by ultrasound 30 d after AI. Effects were considered significant when P <= 0.05, whereas a tendency was designated when P <= 0.10 and P > 0.05. In heifers (Exp. 1.1), incidence of estrus was similar regardless of protocol length (7 or 8 d). There was no independent treatment effect on P/AI or interaction between protocol length and GnRH at AI for P/AI (7d-0: 46.9, 7d-G: 51.4, 8d-0: 47.7, and 8d-G: 43.6%). Heifers in estrus had greater P/AI, and GnRH had no additional effect. More cows (Exp. 1.2) from the 8 d protocol were in estrus than cows submitted to the 7 d protocol. Additionally, despite no interaction between protocol length and GnRH on P/AI (7d-0: 55.9, 7d-G: 60.9, 8d-0: 56.2, and 8d-G: 60.8%), GnRH at AI increased P/AI. There was no interaction between estrus and GnRH, but cows displaying estrus had greater P/AI. Cows not expressing estrus tended (P = 0.06) to have greater P/AI when receiving GnRH. In Exp. 2, more 9 d cows were in estrus than 7 d cows. Protocol length did not affect P/AI but tended (P = 0.08) to interact with GnRH (7d-G had greater P/AI {[}57.9%] than 7d-0 {[}47.6%], but 9d-0 {[}54.6%] and 9d-G {[}55.4%] were not different from other groups). Moreover, GnRH increased P/AI only for the 7 d protocol. No interaction between estrus and GnRH was detected but estrus improved P/AI, and GnRH tended (P = 0.09) to improve P/AI of cows in estrus. In conclusion, despite longer protocols being more conducive to expression of estrus, there were no detectable effects of protocol length on P/AI. In addition, GnRH at FTAI may improve fertility in cows, particularly when cows are treated with shorter protocols. (C) 2020 Elsevier Inc. All rights reserved. (AU)

• FAPESP's process: 18/03798-7 - Studies on ovarian and uterine physiology and improvement of Assisted Reproduction Technologies to increase reproductive efficiency in cattle
• Grantee: Roberto Sartori Filho
• Support Opportunities: Research Projects - Thematic Grants