Body Temperature Variations in Dairy Cattle during the Estrous Cycle and Pregnancy

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Abstract
Daily body temperatures were taken vaginally in 24 cows for a total of 54 cycles. The temperatures were found to fluctuate with the estrous cycle, being lowest just before heat, high on the day of heat, low again at the time of ovulation, and high during the luteal phase of the cycle. Observations were also made on 9 cows in the terminal stage of pregnancy; a precipitous decline in body temperature indicated the imminence of parturition. When progestational steroids were administered to spayed cows, the resultant thermogenic responses suggested that endogenous progesterone elaboration is responsible for the cyclic and pregnancy body temperature variations. Body temperature observations may provide a useful indicator of corpus luteum activity in the bovine.