Environmental and management factors affecting estrous activity in dairy cattle.

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.

Interrelationships with estrous behavior and conception in dairy cattle.

A total of 199 inseminations and estrous periods of lactating cows and heifers of breeding age were used to assess behavioral, productive, environmental, and hormonal events at first observation of estrus and those 12 h later with concurrent breeding efficiencies. Cattle were observed twice daily for estrus, and blood samples were collected at the initial observation of estrus (0 h) and at 12 h. Fifty-one percent of the cattle first were detected in estrus in the morning.

Rates of conception by artificial insemination of dairy cattle.

Over 41 mo, 1004 first and second service inseminations were evaluated in Holstein cows and heifers of breeding age. Cattle were inseminated either at the end of the heat check in which they were observed in heat (0 h) or at the end of the next heat check (12 h). Rate of conception was affected by estrous behavior at 12 h, site of semen placement in the reproductive tract, sire, and environmental temperature the day after insemination.

Effect of prepartum selenium-vitamin E injection on time for placenta to pass and on productive functions.

The effect of a single injection of selenium-vitamin E containing 21.9 mg sodium selenite upon time for placenta to pass following calving and on subsequent reproductive and lactational performance was evaluated. Incidence of retained placenta was 11.