Physiologic response to intense summer heat and its effect on the estrous cycle of nonlactating and lactating Holstein-Friesian cows in Arizona
Wolff, L.K.; Monty, D.E.
American Journal of Veterinary Research 35(2): 187-192
1974
ISSN/ISBN: 0002-9645 PMID: 4855914 Document Number: 74712
Rectal temperatures of lactating cows increased significantly during hot weather to an average peak of 40.1 deg C, whereas the rectal temperatures of non-lactating cows did not increase during the hot season and averaged only 38.9 deg C. The body temperature of many heat-stressed lactating dairy cows began to increase when environmental temperatures exceeded 30 deg C; however, a similar increase did not occur in heat-stressed, non-lactating cows. Both non-lactating and lactating cows had significant increases in respiration in response to hot weather; however, the lactating cows showed a much greater response. Heart rates decreased in both lactating and non-lactating cows during hot weather. Skin temperatures varied more directly with microenvironmental temperature. Intrauterine temperatures were slightly greater than rectal temperatures during cool and hot weather in both non-lactating and lactating cows. Oestrous cycle length, ovulation time, and corpus luteal development were not affected by hot weather in either lactating or non-lactating cows. The duration of oestrus was significantly decreased, however, in lactating cows during hot weather, but not in non-lactating cows.