Estrus Expression and Its Impact on Fertility in Zebu Cows Undergoing Fixed-Time Artificial Insemination

This study aimed to evaluate the effect on fertility throughout the breeding season in Nellore females subjected to time artificial insemination (TAI). A total of 658 multiparous, 138 primiparous, and 257 heifers cows were used. On D0, all females received an intravaginal progesterone-releasing device and E2 benzoate. On D8, the P4 device was removed, and animals received eCG, PGF and E2 cypionate. At this time, all animals were marked with paint between the sacral tuberosity and the tail head. On D10, animals were classified into two experimental groups—With Estrus and Without Estrus—based on the removal of the paint. The overall estrus detection rate (EDR), pregnancy per artificial insemination (P/AI), pregnancy rate from natural mating (P/NM), and final pregnancy rate at the end of the breeding season (P/BS) did not differ among categories. In heifers, estrus expression impacted P/AI (p<0,05). In primiparous cows, no differences were observed for P/AI, P/NM, or P/BS (p>0,05). In multiparous cows the estrus expression influenced P/AI, P/NM, and P/BS (p<0,05). Therefore, estrus detection can be used as a valuable tool to predict FTAI outcomes in heifers and multiparous cows, as well as to forecast overall reproductive performance during the breeding season in multiparous cows.