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Virginia Cooperative Extension - Knowledge for the CommonWealth

The Cow-Calf Manager

Livestock Update, May 2001

John Hall, Extension Animal Scientist, Beef, VA Tech

New Estrus Synchronization Systems Successful in Virginia

Breeding season is upon us. Commercial beef producers need to consider adding artificial insemination and estrus synchronization to their technical toolbox. Until recently, the rewards of engaging in an estrus synchronization and AI program were not sufficient to offset the time and labor involved. Folks that produce commercial replacement heifers or producers that retained ownership through the feedlot obtained the benefits of an AI program with significantly higher prices for their products. However, for the average beef producer, the rewards of better genetics in the cow herd or higher weaning weights were not tangible enough to consider AI.

Then along came programs like the Central Virginia Cattlemen's Association or Buckingham Cattlemen's Association where large numbers of cows are synchronized and artificially inseminated by a technician. The resulting calf crops are grouped and sold in truckload lots at a considerable price advantage. In addition, these groups are building a reputation for uniform high-quality calves.

Why couldn't we do this before?

The problem with older estrus synchronization systems was they only synchronized heat. They did not synchronize ovulation. In order to get good pregnancy rates, producers had to check heat for 5 to 7 days and breed cows 12 hours after heat. That meant gathering cows 2 to 3 times to synchronize and then pulling groups of cows out of the herd to be bred twice a day for 5 days. This is a lot of work for a small operation with only a few cows and little labor. In addition, AI technicians did not want to come out to only breed only a few cows each trip.

Unless you were a purebred producer or a large commercial producer often the costs in time and labor were too high. In addition, the cash costs on a per cow basis were too high as well. Finally, most part-time producers did not feel they could take-off of work for an AI program.

How come these associations can use AI now?

First, the producers were progressive enough to see the advantages of AI in a commercial setting. Second, new estrus synchronization programs came along to allow large numbers of cows or heifers to be timed inseminated with excellent AI pregnancy rates.

GnRH Products Available


Remember you must buy these products through your veterinarian.

These new systems use GnRH (See insert at right), a hormone naturally produced in cows that causes the cow to release of another hormone -LH. LH causes the growth of ovarian follicles and ovulation. Ovarian follicles contain the developing egg. The new GnRH systems synchronize follicular growth and ovulation so all cows ovulate within a very short time. Since ovulation is now synchronized, all the cows in the herd can be bred by timed-AI in one or two trips. This means groups of producers in an area can synchronize their cows at the same time and hire a technician to breed large numbers of cows over 3 to 7 days. Many of the programs mentioned have bred 500 to 1200 cows in a few days on 10 or more farms. However, you can use these systems even if you aren't in a group of producers.

How the systems work

These GnRH based synchronization systems are illustrated in Figure 1. Ovsynch and CO-Synch are timed AI systems where as Select-Synch requires heat checking. All systems start with a shot of GnRH (100 ug) to synchronize follicular growth and then 7 days later give prostaglandin (PGF) like Lutalyse or Estrumate to bring the cows into heat or pre-heat. In Ovsynch and CO-Synch , a second shot of GnRH causes ovulation. In Select-Synch, cows ovulate naturally, but over a longer period of time - 2 or 3 days.


Figure 1. Time lines for GnRH Based Synchronization Systems

There are a few tricks with these systems to maximize pregnancy rates. First, cows on the Ovsynch program should be inseminated 16 to 18 hours after the second GnRH. This means the second GnRH injection should be given in the afternoon. Also, don't be concerned if you don't see many cows in heat on Ovsynch or CO-Synch. The GnRH will actually cause ovulation before the cow even knows she's in heat.

Example of Schedule for Ovsynch
Saturday, May 5 - Inject GnRH
Saturday, May 12 - Inject PGF
Monday, May 14 (pm) - Inject GnRH
Tuesday, May 15(am) - Breed cows

Next, with all these systems, about 8 to 15% of the cows will show heat early. These cows should be inseminated 12 hours after standing heat. This will insure maximum pregnancy rates.

CO-Synch works best if you wait until 64 hours after the prostaglandin shot to give GnRH and breed. Remember you must breed any cows that come into heat early. Often many of these will need inseminated at the same time as the cows that are timed bred.

Finally, these systems do not work well in virgin heifers. The GnRH systems should only be used on mature cows. However, the GnRH systems will jump-start non-cycling cows.

Results with GnRH Systems in VA

Over the last 3 years, my graduate students, Dr. Dee Whittier and I have conducted trials with the GnRH synchronization systems in over 1000 cows in Virginia (Table 1). Some of these cows were given older synchronization systems like Syncromate-B or two shots of Lutalyse. A few of the non-GnRH systems are not shown because of too few cows in the system or only one farm was used, so the results would not be meaningful. In all cases, the GnRH systems out performed the older systems in cows nursing calves.

Table 1. Results from On-Farm Synchronization Trials in Virginia 1999-2001*
System Number of Cows
Synchronized		 % Pregnant to
Single AI		 Range in % Pregnant
to Single AI
Syncromate-B 78 48.7 37.5 ­ 56.5
CO-Synch 64 299 49.8 43.6 ­ 58.8
Ovsynch 291 55.3 40.0 ­ 65.1
Select-Synch 97 62.9 52.9 ­ 71.0
*Note Select-Synch and Syncromate-B cows were bred 12 hours after heat.

CO-Synch and Ovsynch were more consistent than the other systems. The low pregnancy rate herds in each of those groups resulted from problems with body condition of cows or semen quality. However, these low pregnancy rate herds were included in the average and presented as a reminder of other factors that affect AI pregnancy rates.

Another advantage to the GnRH systems is a reduction in the length of the calving season. Herds with cows in good body condition report that 75% to 85% of the cows calve in the first 30 days of the calving season after GnRH synchronization. Many of the cows that did not get pregnant to AI became pregnant to their first service by the clean-up bull. Also, producers report overall pregnancy rates of 85% to 98%.

As the industry continues to change, a greater value will be placed on AI calves. This year would be a good year to try one of the GnRH synchronization systems. Talk to your AI breeding representative or Extension Animal Science Agent about these systems.



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