Abstract
One thousand periods of estrus of Holstein and Jersey cows and heifers of breeding age during 27 mo were used to evaluate environmental and management factors related to estrous behavior during twice-daily heat checks. Mounting activity at the first observation of estrus was influenced by sire within genetic selection group for milk yield, lactation number, primary housing location, time of day estrus first observed, and maximum temperature the day of estrus. Mean number of times an estrous cow was mounted increased from 6.0 mounts/h in the morning to 7.7 mounts/h in the evening. Barn-housed cattle had 8.7 mounts/h compared to 6.1 and 5.5 for dry-lot and pasture groups. Estrous activity was least for heifers and increased for older cows. Mounting activity increased with increasing maximum daily temperature to approximately 25°C. Only 17.7% of the cattle initially observed in estrus displayed mounting behavior at the 12-h heat check. Estrous activity at 12h was affected by lactation number and genetic grouping. Daily milk production near estrus was associated with longer duration between heats but had no effect on conception. Lactation number and service number were related to fertility.
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