Residual Effects of Heat Stress on Lactating Holstein Cows During Post-Heat Recovery

Heat stress is frequently associated with reduced dry matter intake (DMI), milk yield, and physiological alterations in Holstein dairy cows. The aim was to evaluate how prior exposure to heat stress affects feed intake, milk production, energy balance, blood metabolites, and infrared thermography, with special emphasis on the cows’ ability to recover and re-establish normal physiological and productive responses. Thirty multiparous lactating Holstein cows (days in milk = 87 ± 19.6 days) and previous milk yield (30.8 ± 3.95 kg/d) were monitored over 21 days, divided into three 7-day phases: thermoneutral (TN), cows kept at a constant temperature–humidity index (THI) of 69; heat stress (HS), cows at a THI of 82 for 9 h and 69 for 15 h, and recovery (REC), cows at a constant THI of 69. Milk yield decreased by 16.1% during HS and remained 17.3% lower during REC compared with TN. Dry matter intake was reduced by 5.8 and 4.2 kg/d for HS and REC compared to TN cows. Plasma insulin was higher in REC compared to HS. Under the conditions of the present study, heat stress was associated with impaired productive performance, altered metabolism, and changes in the physiological status of mid-lactation Holstein dairy cows, with some effects persisting after the cows returned to thermoneutral conditions.