Abstract
Fourteen lactating Holstein cows were observed between 40 and 150 d postpartum to identify physiological and behavioral changes associated with the day of estrus. Ovulation was predicted on 29 occasions from changes in concentrations of progesterone in milk. Estrus was detected by casual observation by the herdsperson 22 times, but only 13 were detected during a daily 30-min exercise period with an androgenized heifer. Morning milk yield and daily feed intake decreased on the day of estrus. Rectal temperature, afternoon milk yield, and number of changes in postural position during the previous night increased on the day of estrus. When an increase greater than one standard deviation from the within-cow mean was considered evidence of estrus, all measures indicated more false positives than true positives. A combination of elevated temperature, increased changes of postural position at night, and depressed feed intake accurately predicted estrus, but only on 6 occasions out of 29.
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