Whether you are striving to raise elite seedstock or high-quality commercial calves, a major goal of your operation is – or should be – getting as many cows pregnant as early in the breeding season as possible. Estrus synchronization protocols are a proven tool to do just that. These protocols skew the distribution of when cows conceive during the breeding season, and use of the right protocol can offer the opportunity to carry out an artificial insemination (A.I.) program in a straightforward manner. What genetics could you access in a straw that you might not otherwise be able to purchase on the hoof?
In our program at the University of Missouri (MU), we have placed a high level of emphasis on research efforts to better control the estrous cycle prior to fixed-time A.I. One protocol with which we have found great success is the 7 & 7 Synch protocol. In the past two years, this protocol has been widely adopted across the U.S. – and in some locations abroad – as a method to improve conception rates resulting from A.I. in postpartum beef cows.
Estrus synchronization protocols have been used to facilitate the use of reproductive technologies for decades, so what’s the benefit of a new protocol? When protocols are used to enable use of fixed-time A.I. or embryo transfer (ET), the goal is to generate a fertile, highly synchronous period of estrus expression among the largest possible proportion of cows. Cows expressing estrus are more likely to conceive in fixed-time A.I., and recipients that express estrus are better candidates for ET. Results from extensive evaluations indicate that 7 & 7 Synch achieves this goal with significant increases in both the proportion of cows expressing estrus and the number becoming pregnant as a result of either A.I. or ET. With just one additional shot and one additional handling of cows compared to the standard 7-day Cosynch + CIDR protocol, the increased pregnancy rates achieved with 7 & 7 Synch make it an attractive option for producers in many contexts.
How it works
Many protocols for control of the bovine estrous cycle rely upon an initial administration of gonadotropin-releasing hormone (GnRH) to induce ovulation. However, administration of GnRH at a random stage of the estrous cycle only results in ovulation in approximately two-thirds of cows (sometimes less), as successful induction depends on the presence of a physiologically mature follicle. Since a mature follicle is only present during certain windows of time within the estrous cycle, it is not guaranteed that a cow will ovulate when GnRH is administered. In cases in which ovulation is successfully induced, a new or accessory corpus luteum (CL) is formed, and a new ovarian follicular wave is recruited after ovulation. However, when ovulation is not successfully induced, little control is afforded over stage of the cycle. That variation among cows’ responses ultimately goes on to result in varied timing of onset of estrus and, as a result, varied timing of ovulation.
With 7 & 7 Synch, a simple single-step approach offers more control over stage of cycle before GnRH administration (Figure 1). At the start of the protocol, a shot of prostaglandin (PG) is given to induce luteolysis, and insertion of a controlled internal drug release (CIDR) device maintains a low level of progesterone, preventing estrus/ovulation as well as atresia of a dominant follicle. This sets up more cows to have a mature follicle present when GnRH is administered, increasing the likelihood of successfully inducing ovulation. From the herd level, greater uniformity in ovarian response among cows leads to a larger proportion of cows expressing estrus in a very narrow window of time prior to A.I.
Phew, that’s a mouthful of physiology! The bottom line is that more cows are in heat over a short time period. That’s a good thing if performing timed A.I. or if intending to transfer embryos.
Results with 7 & 7 Synch
Large-scale field trials conducted in our program at MU compared the use of 7 & 7 Synch to the commonly used 7-day Cosynch + CIDR protocol. A collaborative trial with Cross Country Genetics of Westmoreland, Kansas, evaluated efficacy in ET recipients on 13 producer operations with over 1,300 postpartum beef cows. With 7 & 7 Synch, 86% of cows expressed estrus following synchronization, compared to the 76% observed with the 7-day Cosynch + CIDR. Of those synchronized with 7 & 7 Synch, 40% became pregnant following ET compared to the 34% of 7-day Cosynch + CIDR synchronized cows that became pregnant.
A follow-up trial in our program evaluated field fertility of both sex-sorted and conventional semen for A.I. of over 1,500 postpartum beef cows in 11 herds across multiple states. Following 7 & 7 Synch, 82% of cows expressed estrus prior to fixed-time A.I. compared to 64% of cows following the 7-day Cosynch + CIDR protocol. It is pretty exciting to see that kind of heat response prior to fixed-time A.I., and pregnancy rates did not disappoint. Pregnancy rates to A.I. were 72% with conventional semen or 52% with sexed semen following 7 & 7 Synch, compared to 61% with conventional semen and 44% with sexed semen following the 7-day Cosynch + CIDR protocol.
7 & 7 Synch is now included on the Beef Reproduction Task Force’s list of protocols recommended for fixed-time A.I., available at their website. Although our program’s published research has evaluated 7 & 7 Synch in cows only, research emerging from other programs around the country suggests an opportunity to use the 7 & 7 Synch protocol effectively in heifers as well. For heifers, it is recommended that fixed-time A.I. be performed at 54 hours after CIDR removal and PG, as opposed to 66 hours as recommended for mature cows. Our research program at MU continues to evaluate variations on the 7 & 7 Synch protocol that might improve results in heifers and in challenging classes of cows, so time will tell whether pregnancy rates with 7 & 7 Synch only continue to improve in the coming years.
