Environmental and Management Factors Affecting Estrous Activity in Dairy Cattle

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Abstract
Periods of estrus (1000) 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 1st observation of estrus was influenced by sire within genetic selection group for milk yield, lactation number, primary housing location, time of day estrus 1st 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 .apprx. 25.degree. C. Only 17.7% of the cattle initially observed in estrus displayed mounting behavior at the 12-h heat check. Estrous activity at 12 h 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.