No. Annual synchronization of estrus will not result in fertility problems. The drugs used to synchronize estrus are naturally occurring, are rapidly cleared from the body, and do not impact biological function long term.
Synchronizing estrus in cows and heifers is an effective way to maximize the use of time and labor required to detect standing estrus in cattle. In addition, by using estrus synchronization, more cows can conceive and become pregnant early in the breeding season with no decrease in fertility. Some estrus synchronization protocols can induce estrous cycles and shorten the anestrous postpartum period, allowing cows to conceive earlier in the breeding season. However, when estrus synchronization is used together with artificial insemination, one of the largest factors that influences fertility is efficiency and accuracy of estrous detection. When fertility is defined as the percentage of cows that conceive in the first few days of the breeding season, synchronized cows will have increased fertility compared to non-synchronized cows. When fertility is defined as the percentage of cows that conceive during the first cycle (first 21 to 25 days) of the breeding season, estrous-synchronized females will have similar or better fertility than non-synchronized females depending on the percentage of animals that are anestrous or prepubertal and the synchronization protocol used. Therefore, estrus synchronization can be a tremendous management tool to get more cows pregnant early in the breeding season.
