Does GnRH treatment at TAI regardless of estrus occurrence increase pregnancy rate in crossbred Bos taurus suckled cows?

• Published in: Animal reproduction 2024-01, Vol.21 (1), p.e20230123-e20230123
• Main Authors: Fernandes, Vanessa Silva, Velho, Gabriella Dos Santos, Dos Santos, Mateus Felipe Osório, Evangelista, Kelly Alves, Gasperin, Bernardo Garziera, Pfeifer, Luiz Francisco Machado, Ferreira, Rogério, Gonçalves, Paulo Bayard Dias, Gastal, Gustavo Desire Antunes, Dalto, André Gustavo Cabrera, Rovani, Monique Tomazele
• Format: Article
• Language: English
• Subjects: BIOTECHNOLOGY & APPLIED MICROBIOLOGY; Original
• ISSN: 1806-9614; 1984-3143; 1984-3143
• DOI: 10.1590/1984-3143-AR2023-0123

The impact of GnRH treatment on the day of TAI in beef cows has received limited investigation, especially concerning its association with estrus expression. Consequently, two experiments were conducted to assess the potential of GnRH treatment on the day of TAI to enhance fertility according to the expression or not of estrus in beef cows. Experiment 1 aimed to determine ovulation rate and luteal function, while Experiment 2 aimed to determine the effect of the two GnRH treatment approaches on pregnancy rate. In Experiment 1, multiparous Brangus suckling cows (n = 17) were submitted to an 8-day TAI protocol. Estrus occurrence was evaluated based on chalk removal on D10 (TAI) and cows were assigned to receive GnRH (25µg lecirelin; im) according to the group: GnRH (n = 7), regardless of estrus expression; or selectGnRH (n = 10), only cows not detected in estrus. Ovulation rate occurring until 77h after IVD removal did not differ (p = 0.17) between GnRH (85.7%; 6/7) and selectGnRH (100%; 10/10). Also, corpus luteum size and serum progesterone concentration were not affected (p>0.05) by treatments. In Experiment 2, crossbred taurine suckled cows (n = 384) were submitted to the same protocol as described in Experiment 1 and were randomly allocated to GnRH or selectGnRH groups. There was no difference in P/AI between groups (selectGnRH = 55.6%; GnRH = 54.3%; p = 0.7) 30 days after TAI. As expected, there was a pronounced effect (p