Time lines for application of treatments related to the 5-Day CO-Synch" width="610" />Using hormone-based protocols to synchronize estrus and ovulation in combination with fixed-time A.I. (no heat detection) has become increasingly popular in the commercial beef industry.
However, protocols developed for use in straight-bred English and Continental breeds have generally not performed well in Brahman-influenced cattle, with pregnancy rates to fixed-time A.I. often ranging from 35 to 40 percent. As a result, few commercial cattlemen in the southern U.S. have routinely used these technologies.
One of the most successful Bos taurus-based protocols, the so-called “Five-Day CO-Synch + CIDR,” employs application of a CIDR device plus an injection of gonadotropin-releasing hormone (GnRH) on day zero. The CIDR is then removed on day five, and a double dose (all at once or split into two injections eight hours apart) of prostaglandin (PG) is injected.
Fixed-time A.I. is at 72 hours in conjunction with a second injection of GnRH (Figure 1A). Pregnancy rates to fixed-time A.I. in Bos taurus and Bos taurus crosses have been reported to range from 55 to 60 percent in mature cows and 50 to 55 percent in heifers.
Time lines for application of treatments related to the 5-Day CO-Synch" width="610" />
Unfortunately, this protocol does not result in acceptable fixed-time A.I. pregnancy rates in Brahman-influenced cattle. However, modifications of the procedure, developed at the Texas A&M AgriLife Research Station in Beeville and called Bee Synch, yielded excellent results in these cattle types.
