Synchronization of estrus in dairy heifers: a field demonstration

Use of prostaglandin F2 alpha to synchronize estrus was demonstrated over 3 yr with 2966 dairy heifers in 45 herds. Reproductive status of all heifers was determined before any injections occurred. Anovulatory heifers (8.3%) were not injected or inseminated. Ovulatory heifers received one intramuscular injection and most heifers received two injections of prostaglandin F2 alpha spaced 11 d apart. Observations for estrus and insemination were scheduled and performed by dairy farmers. Insemination of heifers occurred 12 h after detection of estrus or at 80 h after second injection of prostaglandin F2 alpha. Pregnancy rate averaged 50.9% but varied from 0 to 100%. Pregnancy rate after insemination according to estrus (62.8%) was greater than when insemination was at 80 h (39.1%). Low pregnancy rates were associated with limitations in basic management of heifers before or during insemination. Managerial limitations were in timing insemination, range of ages or weights of heifers housed together, number and types of vaccinations, season and diet, frequency of observing heifers for estrus, and number of straws of semen thawed concurrently. Managerial factors that affect fertility are similar whether or not estrus is synchronized. Although agents used to synchronize estrus do not affect fertility directly, managerial limitations on fertility may be accentuated by increased intensity of activity associated with synchronization.