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Copyright © 2015
Angus Journal

Control of Estrus in Cows

Success rate of fixed-time AI protocols makes it harder to justify the time for heat detection.

by Lynsey Meharg for Angus Journal

STAUNTON, Va. (Oct. 15, 2013) — Cliff Lamb of the University of Florida addressed controlling estrus in mature cows during the Applied Reproductive Strategies in Beef Cattle (ARSBC) Sympoisum in Staunton, Va., Oct. 15-16.

Cliff Lamb

“If you’re not going to detect 90% or better of your cows in heat, you might as well go with a fixed-time AI system,” said Cliff Lamb, University of Florida.

To begin, Lamb touched on the differences between synchronization rate, conception rate and pregnancy rate. Synchronization rate, he explained, is the percentage of females detected in estrus compared to the number of females synchronized. Conception rate is the percent of females pregnant vs. the number inseminated, while pregnancy rate is the percent of females pregnant compared to the number synchronized.

Looking at pregnancy rates following breeding at a fixed time vs. breeding following heat detection, Lamb deduced that at a 65% conception rate, a producer would need to detect 90% of cows in heat to achieve satisfactory conception (see Fig. 1).

“If you’re not going to detect 90% or better of your cows in heat, you might as well go with a fixed-time AI (artificial insemination) system,” said Lamb. “You’re not going to get the same percentage of cows pregnant compared to all the cows you synchronized.”

For that reason, Lamb focused his discussion on the two synchronization protocols suggested by the Beef Reproduction Task Force for use with fixed-time AI:

Figure 1Lamb suggested the 5-day and 7-day CO-Synch systems are examples of the trade-offs between results and convenience. Though these methods do require handling the cattle, Lamb cited the advantages and discouraged producers from pursuing other methods.

“Those are the two systems we would recommend for timed AI in beef cattle,” said Lamb. “If you hear of any others, just decide to go back to the protocol sheets and quit listening to those witch doctors.”

With the 5- and 7-day systems, the average conception rate was 58% with the 7-day and 61% for the 5-day. When using these methods, producers must decide whether the extra 3% is worth working the cattle through the chute more times.

To conclude his presentation, Lamb introduced a smartphone app (available in the Google Play Store or Apple iTunes) designed to help producers compare the cost of using AI vs. natural service. Known as the AI Cowculator, the application allows producers to estimate what it would cost to maintain a herd bull compared to what it would cost to AI each female.

Lamb spoke during Tuesday’s ARSBC session focused on management considerations influencing success synchronized AI programs. Visit the Newsroom at to listen to his presentation, view his PowerPoint slides and proceedings paper, or access the synchronization protocols recommended for cows by the Beef Reproduction Task Force.

Comprehensive coverage of the 2013 ARSBC symposium is available online at Compiled by the Angus Journal editorial team, the site is made possible through sponsorship by the Beef Reproduction Task Force.

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