Detection of estrus by radiotelemetric monitoring of vaginal and ear skin temperature and pedometer measurements of activity.

Methods to improve detection of estrus in dairy cows have been studied extensively without wide acceptance of any one method. In the present study, the use of body temperatures and pedometer-monitored activity were evaluated as methods of estrus detection. Twice daily activity levels of 13 lactating cows were monitored using pedometers, and vaginal and ear skin temperature measurements were made continuously using radiotelemetry. Activity increased 2.8-fold at estrus for the 8-h daytime period (0630 to 1430 h), during which cows were given a 5-h turnout period, but not for the 16-h overnight period (1430 to 0630 h), during which cows were confined to tie stalls. When increased activity was used to detect estrus on an individual cow basis, 20 of 25 estruses were detected with 4 false positives. Vaginal temperature increased by .6 +/- .3 degree C at estrus and remained elevated by at least .3 degree C for 6.8 +/- 4.6 h. When increased vaginal temperature was used on an individual basis, 17 of 21 estruses were detected with 3 false positives. Rate of detection of estrus by visual observation was 66%.