ESTRUS SYNCHRONIZATION SYSTEMS: GnRH

Development of methods to manipulate the estrous cycle so that all cows are in estrus during a short, predefined period (synchronized estrus) while maintaining normal fertility has been a difficult goal to achieve, but has resulted in the creation of valuable synchronization protocols that are available to producers today. Although implementation of estrus synchronization and AI will improve the profitability of beef operations, no more than 3 to 5% of all beef operations in the U.S. utilize the technology (Patterson et. al., 2001). The major barriers to utilization of estrus synchronization and AI are time and labor (Kesler, 2003). During the past 25 years, protocols have been developed that minimize time and labor, and yield excellent pregnancy rates. One of the most important steps to creating the wide variety of effective protocols that are available today began with the understanding of follicular waves and the development of the Ovsynch protocol (illustrated in Figure 1). Ovsynch was originally created for use in dairy cattle, however the basic elements (GnRH followed by PGF2α seven days later) have as much value in beef cattle. Three protocols (Select Synch, CO-Synch, and Hybrid Synch) have emerged for use in beef cattle and will be discussed within this manuscript.