Physiologic responses of preparturient and postparturient Holstein-Friesian cows to summer heat stress in Arizona.

A group of 18 Holstein-Friesian cows were studied in central Arizona to evaluate seasonal heat stress factor in preparturient and postparturient dairy cows. Physiologic measurements were made within 2 weeks before calving and within 1 week after calving. The studies were conducted during the cool winter months of December and Janurary and during the hot summer months of July, August, and September. Comparisons were made of rectal temperatures, vaginal temperatures, skin temperatures, respiratory rates, and heart rates between the 2 groups of preparturient and postparturient cows and between the 2 seasons of the year. Rectal temperatures, vaginal temperatures, skin temperatures, and respiratory rates of both preparturient and postparturient cows were significantly higher during the hot weather season than during the cool weather season. Heart rate was not significantly affected by hot weather. The respiratory rates, heart rates, and rectal temperatures of preparturient cows were significantly higher than in postparturient cows during cool weather; however, this relationship was masked by hot weather.