Evaluation of strategies to maximize fixed-time artificial insemination efficiency in Bos taurus indicus ("Nellored") females in Brazilian savannah environment by a real-life study.

Abstract

This study aimed to identify factors and technologies that could enhance the pregnancy rate of "Nellored" females by evaluating the animal category, number of progesterone-releasing intravaginal device (DP4) uses and day of its removal, equine chorionic gonadotropin (eCG) dosage, time of fixed-time artificial insemination (FTAI), melengestrol acetate (MGA®) supplementation (before FTAI in heifers and after artificial insemination in cows), vaccination against reproductive diseases, body condition score (BCS, on a 1-5 scale), month of last calving before FTAI, and estrus expression intensity. Data from 15,618 FTAI procedures conducted across three breeding seasons (October to February of 2016/2017, 2017/2018, and 2018/2019), were evaluated. Multiparous cows showed higher pregnancy rates (45%), compared with primiparous cows (39%) and heifers (29%) (p < 0.05). Pregnancy rates decreased with lower estrus expression scores (51% for score 3, 36% for score 2 and 27% for score 1). The month of last calving before FTAI, period of the day when FTAI was performed, DP4 removal day and vaccination against reproductive diseases did not affect pregnancy rates (p > 0.05). MGA® supplementation before FTAI increased pregnancy rates in heifers from 19 to 34% (p < 0.05). The use of DP4 affected pregnancy rates (p < 0.05); however, its reuse did not have a negative impact. Higher pregnancy rates for FTAI protocols were observed in multiparous cows, animals with high estrus intensity, and a BCS of 2.5 to 3.0. Administering at least 200 IU eCG and supplementing heifers with MGA® through 26th to 13th days before FTAI is recommended.