Estrous intensity and conception rates in Holsteins.

During 34 mo, 732 inseminations were evaluated in Holstein cows and heifers of breeding age. Females were submitted for insemination after detection of either 1) standing estrus, 2) mounting activity, or 3) other subtle symptoms of estrus (clear mucus, general appearance of genitalia or tailhead, and excessive vocalization). Conception rates were similar following standing estrus and mounting activity (50 versus 46%). Although higher conception rates occurred following standing or mounting activity than after detection of subtle estrous symptoms, one of three inseminations resulted in conception after insemination in the latter group. Clear mucus in half of the females upon cervical manipulation at insemination was associated with higher conception. Service number, age, and maximum ambient temperature on day of insemination also affected conception rates. Methods of thawing semen, ease of cervix penetration at insemination, service sire, inseminator, and time of estrous detection and insemination had little effect on fertility. Acceptable conception rates were achieved with more liberal interpretation of estrous symptoms.