The uterine diameter and ovarian activity influence the presence of estrus and pregnancy in beef heifers under a J-Synch protocol for fixed-time artificial insemination

The study assessed how the diameter of uterine horns and cyclical activity in beef heifers influence their estrous behavior and gestation rates with fixed-time artificial insemination (FTAI). A total of 100 B. taurus heifers (undefined crosses of Angus, Charolais, and Gelbvieh) weighing 300 +/- 32 kg were evaluated for their body condition (scale 1 to 5), uterine horn diameter (1: less than 1 cm; 2: 1 to 1.5 cm; 3: greather than 1.5 cm), and cyclical activity at the start of the protocol. Cyclical activity was classified into cycling (C), superficial anestrus (AS), or deep anestrus (AP). The J-Synch protocol was used for ovulation synchronization, with estrous activity monitored through paint at the base of the tail. The results showed that 81% of the cyclin (C) heifers exhibited estrus within 72 hours of completing the protocol, significantly surpassing AS and AP heifers (P <= 0.001). P <= 0.001). The presence of estrus in heifers with a larger uterine diameter was higher than in those with a smaller diameter (P <= 0.001). P <= 0.001). Additionally, the intensity of estrus significantly influenced gestation rates 30 days post-FTAI (P <= 0.003). P <= 0.003). Cyclical activity and the diameter of the uterine horns at the start of the treatment also affected pregnancy rates (P <= 0.05). P <= 0.05). In conclusion the uterine horn diameter and initial cyclical activity in beef heifers impact their response to the J-Synch protocol and the rates.