Effects of temperature on cattle

A study of 159 Gyr crossbred dairy cows under tropical conditions in Peru compared two estrus synchronization protocols (conventional PC9 vs. extended J-Synch6) for follicular timed induction (FTAI) and evaluated their relationship with heat stress index (THI) in seven critical phases of the program. Both protocols showed similar estrus and pregnancy rates, but J-Synch6 produced larger preovulatory follicles, and its estrus manifestation was more sensitive to hours without heat stress (THI < 72) and to stress peaks (THI ≥ 83) during the follicular growth phase (Vásquez et al., 2025).