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. Service number, time of day at which insemination occurred, inseminator, and timing of insemination in relation to the onset of estrus had no effect on fertility. With twice daily heat checks, a single daily service produced acceptable rates of conception.