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Split-time Protocols Offer Savings

The most recent advancement in synchronized AI protocols reduces GnRH use, times breeding in two groups based on observation of estrus.

by Shauna Rose Hermel, editor

Producers can save labor and expense with their synchronized timed artificial insemination (AI) program if they use a split-time AI approach, said David Patterson, state beef extension specialist and professor of animal science at the University of Missouri–Columbia.

David Patterson The University of Missouri’s David Patterson shared the evolution of estrous synchronization protocols, culminating in split-time artificial insemination protocols for heifers and cows.

During the 2017 Applied Reproductive Strategies in Beef Cattle Symposium in Manhattan, Kan., Patterson shared the evolution of estrous synchronization protocols, providing an overview of the advancement in products and technologies since the 1950s. Included were brief discussions of current protocols recommended by the Beef Reproduction Task Force for use in synchronizing estrus in beef heifers and mature cows.

One of the more recent advancements has been the evolution of split-time AI (STAI) protocols evaluated by Jordan Thomas, a doctoral candidate advised by Patterson within MU’s Division of Animal Science.

With the initial goal of trying to improve pregnancy rates using sexed semen in a fixed-time AI program, Thomas evaluated whether pregnancy rates among cows subjected to fixed-time AI (FTAI) could be improved by delaying the timing of AI on those cows that had not exhibited heat by the standard AI time. The thought was that this would better align the window of sperm fertility with the timing of GnRH-induced ovulations.

Using the 7-day CO-Synch + CIDR protocol, cows exhibiting estrus were inseminated according to the FTAI schedule, while those not exhibiting heat were inseminated 20-24 hours later. All cows were administered gonadotropin-releasing hormone (GnRH) at 66 hours. Better overall pregnancy rates were achieved.

In subsequent trials Thomas evaluated the STAI protocol using conventional semen to breed heifers following administration of the 14-day CIDR-PG protocol and then thirdly using conventional semen to breed mature cows with the 7-day Co-Synch + CIDR protocol.

The take-home messages from Thomas’s work, Patterson said, include:

• Split-time AI increased pregnancy rates by 34% among non-estrous cows inseminated with sex-sorted semen.

• Split-time AI increased pregnancy rates by 15% among non-estrous heifers using conventional semen.

• No significant improvement in pregnancy rates was observed with split-time AI using conventional semen in non-estrous cows.

A series of three follow-up studies conducted by Brianne Bishop at MU showed that it is not necessary to administer GnRH to heifers or cows that express estrus up to 66 or 90 hours after prostaglandin following administration of the 14-day CIDR-PG protocol in heifers or the 7-day CO-Synch + CIDR protocol in cows. GnRH may be administered concurrent with AI for heifers or cows that fail to express estrus prior to 90 hours, which minimizes use of GnRH and results in a greater overall estrous response in cows.

Patterson said Bishop’s research showed that the higher pregnancy response rates to STAI vs. FTAI were due primarily to higher estrous response rates rather than the timing of insemination relative to GnRH-induced ovulations.

The split-time approach affords beef producers the opportunity to increase pregnancy rates resulting from AI.

For more details of Patterson’s presentation, refer to his PowerPoint and proceedings posted to the Newsroom at, which features comprehensive coverage of the symposium. Compiled by the Angus Journal editorial team, the site is made possible through sponsorship by the Beef Reproduction Task Force. To access video of the presentations, visit the Beef Reproduction Task Force page on Facebook.

Hosted by the Task Force and Kansas State University Research & Extension, the 2017 ARSBC Symposium was convened Aug. 29-30 in Manhattan, Kan. Next year’s symposium will be Aug. 29-30 in Ruidoso, New Mexico.

Editor's Note: This article was written under contract or by staff of the Angus Journal, an Angus Media publication. To request reprint permission and guidelines, contact Shauna Rose Hermel, editor, at 816-383-5270.