DOI: https://doi.org/10.5513/JCEA01/26.3.4587

2025, 26 (3)   p. 564-572

Cyndi HERNÁNDEZ-CORONADO, Rene CALDERÓN-ROBLES, Ana ROSALES-TORRES, Ricardo FAUSTINO-CARMONA, Adrian Guzmán-Sánchez

Abstract

To evaluate if the ovulatory inducer, the genotype, and their interaction affect the reproductive response to a fixed-timed artificial (FTAI) protocol and to determine whether this protocol improves the breading season pregnancy rate (PR), a total of 242 Brahman and 155 Brahman by Brown Swiss cows (F1) were used in this experiment. Cows in the control group (153 Brahman and 115 F1 cows) did not receive hormonal treatment, whereas the estradiol cypionate (EC; 45 Brahman and 19 F1 cows) and the GnRH groups (44 Brahman and 21 F1 cows) were subjected to an estradiol-based FTAI protocol and received EC or gonadotropin-realising hormone (GnRH) to induce ovulation. Brahman cows treated with EC had a higher pregnancy per artificial insemination (P/AI; P<0.05) than Brahman cows treated with GnRH, but not with F1 cows treated with GnRH or EC. The breeding season PR in synchronized cows was greater (P<0.001) than in control cows, although there was an interaction (P<0.05) between groups and genotypes. In Brahman cows, the use of EC (P<0.001) but not GnRH increased the breeding season PR compared with control cows, but in F1 cows, only the use of GnRH to induce ovulation increased (P<0.001) the breeding season PR compared with the control cows. In conclusion, GnRH is the best option to induce ovulation and improve the P/AI in an estradiol-based FTAI protocol, but the breeding season pregnancy rate in Brahman cows could be compromised with the use of this hormone. Additionally, hormonal treatment improved breeding season PR compared with untreated animals.

Keywords

FTAI protocol, beef cattle, cyclicity, P/AI, GnRH

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