Heat stress on milk production and milk protein content in Friesian cows

The effect of heat stress on milk production and milk protein content in Friesian cows were studied in herds in Andalucia, southern Spain a region with very hot and dry summers. In this season, mean values of dry bulb (T-db) temperature and temperature humidity index (THI) exceeded those normally considered critical for dairy cows, during the day, but not at night. A study in 44 herds of lactation yield in relation to month of calving showed significant differences associated with month of calving (P<0.05). Cows calving in late summer and autumn produced less than those calving in winter and spring. Data on milk protein content collected in 6 herds in 3 years, were analysed. Milk protein contents were lower during the hottest months.