Maternal bovine appeasing substance analog mitigates the effects of excitable temperament on timed artificial insemination outcomes in Nellore cows.

This study evaluated whether a synthetic analog of maternal bovine appeasing substance (mBAS) can mitigate the negative effects of excitable temperament on reproductive outcomes in Nellore cows subjected to timed artificial insemination (TAI). Two experiments were conducted using a 10-day synchronization protocol, where day 0 (D0) marked the start of the hormonal ovulation synchronization and day 10 (D10) was the day of TAI. Experiment I (n = 87) assessed the effects of mBAS on preovulatory follicle (POF) characteristics, follicular blood flow, cortisol concentration, and ovulation, with ultrasonographic evaluation of POF conducted on D10. In Experiment II (n = 597), cows were classified based on temperament into adequate or excitable categories, as determined by subjective behavioral evaluations in the chute and exit scores recorded during handling. mBAS was administered on days 0 and 10 of the protocol. Although mBAS did not significantly alter POF volume or Doppler pixel intensity, mBAS-treated excitable cows exhibited lower cortisol concentrations at TAI compared to controls (18.7 ± 2 vs. 28.5 ± 4 ng/mL; P = 0.02). Conception rate (CR) was higher in the mBAS group (66.9% vs. 63.0%; P = 0.04), largely due to improved fertility in excitable cows (68.1% vs. 52.9%; P = 0.03). Pregnancy loss (PL) tended to be lower in treated cows (2.0% vs. 4.4%; P = 0.07). These findings provide early evidence that mBAS enhances fertility in Bos indicus cows by reducing stress responses in behaviorally reactive individuals, supporting its use as a management tool to increase reproductive efficiency in TAI programs.