Changes throughout estrous cycles of variables that might indicate estrus in dairy cows.

Two experiments examined physiological changes throughout estrous cycles of Holstein cows. In experiment one, changes were characterized for physical activity, vaginal pH, vaginal temperature, milk yield, heart rate, and concentration in blood plasma of progesterone and 13,14-dihydro-15-keto-prostaglandin F2 alpha. Variables were measured daily in 11 cows through a total of 28 estrous cycles. Cows in estrus at least once postpartum were used. Observations for estrus were at least twice daily. Variables changed significantly with day of estrous cycle. Changes of progesterone, physical activity, and 13,14-dihydro-15-keto-prostaglandin F2 alpha were more marked around estrus than were changes of the other variables. Peaks of physical activity coincided with estrus in 75% of the cases. Experiment two was to determine if increased physical activity, measured with pedometers, coincided with estrus in commercial dairy herds. Cows on 14 farms in New York were fitted with mechanical pedometers, and the pedometers were read at each milking. Readings from 3 days before until 3 days after estrus were used from 55 estrous periods identified by the producers. Physical activity was maximal on day of estrus in 73% of the estrous periods. Increased physical activity of commercial dairy cows agreed well with the producers' diagnoses of estrus. Pedometers could be a valuable component of an estrous detection program.