Synchronization of Estrus

Estrous synchronization gives many beef cattle producers the opportunity to capture the economic benefits of artificial insemination (AI). Because AI involves a substantial investment of labor and time, most commercial farms or ranches will not utilize this technology unless this investment can be confined to a period of less than 5 to 7 days. To make the labor requirements of AI compatible with modern beef cattle breeding, the estrous cycle must be synchronized so that a high percentage of treated females show a fertile, closely synchronized estrus. The synchronization of cattle can be achieved by the use of progestogens,1 progestogen-prostaglandin combinations,2 prostaglandins alone,3 progestogen-estrogen combinations,4,5 and gonadotropin-prostaglandin combinations with or without progestogens.6 In order to understand how each of these hormones, and the programs that have been developed around them, work in individual animals and on a herd basis, one must review the physiology of the bovine estrous cycle. Synchronization of estrus utilizing progestogens For many years, progestogens have been known to suppress estrus in cattle an