Detection of estrus was determined by walking activity
recorded by the radiotelemetric pedometer (Gyuho system,
ComTech), as well as visual observation heat-mount detectors
(KAMAR Product Inc., Zionville, IN, USA) and plasma
progesterone concentrations. Estrus based on pedometer
activity was defined as a 1.5-fold increase in the number of
steps over the average number of steps for the previous
2 weeks. The duration of estrus was defined as the period
of increased step rate.