Technical Abstract: Estrous synchronization can be profitable for producers who use natural service as well as AI. Protocols that are used for synchronization should be capable of inducing estrous cycles in the majority of cows within a herd. Synchronization protocols that also induce estrous cycles in anestrous cows provide more opportunities for cows to conceive during a defined breeding season and can result in higher pregnancy rates. In addition, calves that are born early in the calving season are generally worth more at weaning. Melengesterol acetate (MGA) is a feed additive that effectively synchronizes the estrous cycle and induces estrous cycles in virgin heifers when fed for a period of 14 days. The estrus that heifers display within a week after removing MGA is usually subfertile, so bulls should be placed with heifers 12 to 17 days after the last feeding of MGA to breed heifers at the following estrus. This protocol has resulted in 83% pregnancy rates during a 30- day breeding season. For cows, producers should consider using an injection of gonadotropin releasing hormone (GnRH) followed one week later with an injection of prostaglandin (PGF). Bulls are placed with cows anytime after the GnRH injection, but generally 2 to 3 days before the PGF injection. This protocol has increased pregnancy rates by as much as 20%. It is very important that bulls pass a breeding soundness exam prior to being used to breed estrous synchronized cows. The correct bull to cow is not known, but probably lies between 1:15 for virgin bulls to 1:30 for some older bulls.