Modeling changes in rumination time and milk yield to detect the onset of heat stress in lactating dairy cows of different physiological traits.

Identifying early warning signals of heat stress, this study assessed rumination time (RT) and milk yield (MY) to determine critical threshold levels in dairy cows. RT declined at lower temperature-humidity index (THI) values (≈57–62) than MY (≥65), indicating it is an earlier sign of HS. Similarly, shorter HS duration was needed to affect RT than MY. High-producing, multiparous cows in mid-lactation were most sensitive. Both RT and MY decreased progressively after thresholds were exceeded. These findings suggest HS mitigation should begin before THI reaches 57 and be tailored to cow characteristics, emphasizing RT as a sensitive early indicator of heat stress.

By Serviento A.M., Wang A., Chang Y. et al.