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Synchronization of estrus involves methods of manipulating the estrous cycle of females within a herd so they express estrus at approximately the same time. There are several traditional protocols available for synchronizing estrus (heat) among beef cows. Traditional protocols include one or two Prostaglandin protocols, the MGA/prostaglandin protocol and the Syncro- Mate B protocol. None of these methods have been universally adopted because none are able to satisfy all situations. There are also a couple of new protocols that have been developed within the last 2 years that have resulted in higher success than traditional protocols. These new protocols include the use of prostaglandin and GnRH (Gonadotropin Releasing Hormone). The intent of this article is to familiarize the reader with estrous synchronization, review the traditional protocols that are available, and introduce the new protocols for synchronization of estrus.
Estrous synchronization is a useful part of an artificial insemination program because checking for estrus in breeding animals, particularly under range conditions, is time consuming and expensive. Synchronization of estrus allows a producer to schedule labor for the appropriate time during the breeding and calving seasons. Synchronization should result in calves being born earlier in the calving season and thus, older, heavier and more uniform calves at weaning. Cows that calve earlier in the calving season have more time to recover before the start of the subsequent breeding season and thus, are more likely to be exhibiting estrous cycles (cycling) at the start of breeding. Increasing the number of cows cycling at the onset of breeding may translate to higher pregnancy rates and lower heifer replacement rates. The net results of an estrous synchronization program should provide an economic edge to the cow/calf producer by improving herd quality, calf crop uniformity and potentially lower annual production costs.
The success of the estrous synchronization program could depend upon a producer's understanding of how it works. Success may also depend upon the number of cows that are cycling when the protocol is initiated. Within any herd of cows, some of the cows will generally be anestrus at the start of the estrous synchronization treatment. Unless the proper estrous synchronization protocol is chosen, these cows have no chance of responding. The ability of individual estrous synchronization protocols to induce estrous cycles in anestrous cows is mentioned below. Regardless of the estrous synchronization protocol chosen, cows should be at least 30- 40 days since calving at the initiation of treatment.