COLUMBIA, Mo. – A new estrus synchronization protocol evaluated at the University of Missouri greatly improves heat response and pregnancy rates to fixed-time AI in beef cows.

MU Extension beef reproduction specialist Jordan Thomas says results from a recent large field trial found 82% of cows come into heat before the timed AI service using the protocol 7 & 7 Synch. This compares to 64% of cows in heat using the standard 7-Day CO-Synch + CIDR. Cows that come in heat before timed AI generally achieve higher pregnancy rates. “Pregnancy rates with this new protocol are exceptional,” says Thomas.

Over the past two years, graduate students Rachael Bonacker and Carson Andersen in the Thomas lab worked extensively in developing and evaluating the protocol. Andersen led the large timed-AI field trial, with research results across two states, five operations, 11 cowherds and more than 1,500 cows.

Pregnancy rates vary depending on whether conventional or sex-sorted semen was used, but pregnancy rates were improved with both semen types using the 7 & 7 Synch protocol.

Using a single fixed-time AI service, 72% of cows on 7 & 7 Synch became pregnant to timed AI using conventional semen. When sex-sorted semen was used, pregnancy rates to timed AI dropped to 52% after 7 & 7 Synch. “The pregnancy rate was lower with sex-sorted semen, but still quite good,” says Thomas.

This compares to pregnancy rates after the standard 7-Day CO-Synch + CIDR protocol of 61% with conventional and 44% with sex-sorted semen.

“These levels of improvement, regardless of the semen type used, are very exciting,” says Thomas. “With the consistency of the results we have seen and the early reports from producers using this protocol, we are very comfortable with this as a new recommendation for broader use.”

The 7 & 7 Synch method improves ovarian follicular maturity before the administration of gonadotrophin-releasing hormone (GnRH) typically given at the beginning of an estrous cycle control program. This new protocol accomplishes that by treatment with prostaglandin F2a and an intravaginal progesterone insert (CIDR) in advance of GnRH. This enhances the uniformity of cows’ response to the protocol, thereby improving overall control of the estrous cycle compared to standard 7-Day CO-Synch + CIDR protocol.

Before Andersen’s large field trial evaluating this protocol on producer herds, a more mechanistic experiment led by Rachel Bonacker provided rationale for the treatment schedule.

Other members of the team included graduate students Katy Stoecklein, Cameron Locke, Jaclyn Ketchum and Emma Knickmeyer, as well as MU Extension dairy veterinarian Scott Poock. Extension livestock specialists Zac Erwin, Jenna Monnig, Andy McCorkill and Eldon Cole also played key roles on producer locations and at the MU Southwest Research Center.

Bonacker presented her work in 2019 the American Society of Animal Science annual meeting and the Applied Reproductive Strategies in Beef Cattle conference. Andersen’s results have been accepted for presentation in abstract form at the International Congress on Animal Reproduction next year in Bologna, Italy. Bonacker also led a large field trial evaluating the new 7 & 7 Synch protocol among recipient beef cows in an embryo transfer program, also with improved results. That abstract also was accepted for presentation at the meeting in Bologna.

“We are just really excited to share a new protocol that can benefit producers across the country,” says Andersen. “Nothing is more rewarding than seeing research that can increase profitability and productivity get implemented on the farm.”

The Thomas lab works to improve the profitability and sustainability of beef cattle production systems through extension, education and applied research. For more information, contact Thomas at or connect with the Thomas lab’s “Mizzou Repro” pages on social media.