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Angus Journal
Copyright © 2015
Angus Journal

Control of Estrus in Cows

Timed AI protocols for cows offer advantages in management, calving distribution and economics..

SIOUX FALLS, S.D. (Dec. 3, 2012) — In outlining estrous synchronization protocols for cows, Cliff Lamb, University of Florida North Florida Research and Education Center, focused on those protocols designed for use with fixed-time artificial insemination (AI).

Cliff Lamb

Cliff Lamb

The comfort level with using these programs without heat detection has increased, Lamb told those in attendance at the 2012 Applied Reproductive Strategies in Beef Cattle (ARSBC) symposium in Sioux Falls, S.D., Dec. 3-4. “I would almost bet that 60% to 70% of the people who use estrous synchronization right now utilize fixed-time artificial insemination.”

Lamb said he always refers people to the protocols recommended by the Beef Reproduction Task Force. The task force regularly reviews protocol options and publishes a two-page flier that on one side lists recommended synchronization protocols for cows and on the other lists recommended protocols for heifers. Some of the protocols do include heat detection. (Click here to download Fig. 1, the 2013 protocols.)

In evaluating estrous synchronization protocols, Lamb reviewed three definitions:

Lamb asked attendees to imagine they synchronized 100 cows. They then detected 75 of those cows in heat. This meant their synchronization rate was 75% (75 ÷ 100). Those 75 cows were bred, resulting in 50 pregnancies for a conception rate of 67% (50 ÷ 67).

“That’s usually what most people go to the coffee shop about,” said Lamb, emphasizing that this is not the true pregnancy rate as it forgets about the cows that weren’t detected in heat or that weren’t bred.

Pregnancy rate, he explained, is the percentage of females that become pregnant compared to the total number of females that were synchronized. In the example, of the 100 females synchronized, 50 became pregnant, resulting in a 50% pregnancy rate (50 ÷ 100).

“If you truly want to evaluate the success of the system in your own operation, utilize pregnancy rates and don’t utilize conception rate,” Lamb said. “You can still go to the coffee shop and boast about your pregnancies, but when you get home, take a real look at it.”

Lamb used Fig. 2, below, to illustrate why he prefers to rely on Timed AI rather than heat detection. TAI protocols on cows regularly achieve pregnancy rates of 58%, Lamb said, illustrating his preference for using the technology. To accomplish the same success breeding on heat detection, you’d have to detect heat in 90% of your cows and get a 65% conception rate.

Click here to view larger image of Fig. 2: Effect of
synchronization rate on pregnancy rates.

Recommended protocols

The two protocols Lamb recommended for fixed-time AI (TAI) for cows were the seven-day CO-Synch + CIDR® and the five-day CO-Synch + CIDR systems.

Lamb explained that the seven-day system requires an injection of gonadotropin-releasing hormone (GnRH) as CIDRs are inserted. After seven days, an injection of prostaglandin (PG) is administered as CIDRs are pulled. Sixty to 66 hours later, the cows are given another shot of GnRH as they are AIed. Essentially, you handle the cows three times.

“The great thing about a timed AI protocol is you can plan three months from now what day you want to AI your cows and at what time you want to do that, because there is no heat detection here at all,” Lamb said.  

The five-day system is very similar to the seven-day system, he explained. You give an injection of GnRH when you insert the CIDR. You pull the CIDR five days later, giving an injection of PG. Eight hours later, run the cows through the chute again and give a second injection of PG. AI the cows 72 hours after pulling the CIDRs. At breeding, give an injection of GnRH.

Each system has its drawbacks, said Lamb. However, the overall impact of TAI is much greater than a few potential risks in the TAI process.

When questions arose as to a decrease in percentage coming in heat in the first 21 days after a TAI breeding compared to the following 21 days, researchers conducted a study in which cows were synchronized but not bred. Return rates during the next 21 days were normal, indicating it was not a case of the protocol “messing up” the cows’ heat cycles. Factors that might be playing a role, Lamb explained, include early embryonic loss during the first 21 days and whether bulls were ready to handle synchronized returns.

Economically, Lamb said, using TAI results in calves born earlier in the season on average, higher overall pregnancy rates, higher weaning rates, and heavier weaning weights (per cow bred). Put into an economic model that assumed a bull price of $3,250 per bull, a salvage bull price of $75 per hundredweight, bull maintenance costs of $365 per year, 7% interest, selling price of $121 per cwt. for 550-pound (lb.) steer calves, semen cost of $13 per dose and a reduction in the required bull-to cow ration of 1:17 to 1:34, Lamb estimated an advantage of $49.14 per cow exposed to TAI.

Lamb spoke during Monday's ARSBC session focused on the importance of estrus. For more information, visit the Newsroom at to listen to his presentation and to view his PowerPoint slides and proceedings paper.

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

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.