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Virginia Cooperative Extension -
 Knowledge for the CommonWealth

The Cow-Calf Manager:
Estrus Synchronization Systems
for Virginia Cow/Calf Operations

Livestock Update, May 2000

John Hall, Extension Animal Scientist, Beef, Virginia Tech

Breeding season is just around the corner, and more and more producers need to begin looking at artificial insemination as a tool that they are going to use. Several producer groups like the Central Virginia Cattlemen and the Buckingham Cattlemen's Association have demonstrated the power of using AI. These cattlemen work together to select a few AI bulls, breed their cows and then group market the resulting calf crop. One of the keys to successful AI in a commercial operation is a reliable estrus synchronization program.


Over the past 2 years, Dr. Dee Whittier and I along with our graduate students have conducted on-farm estrus synchronization research under typical VA field conditions. Based on observations from over 600 cows at 6 different locations the two most promising systems are Ov-synch and CO-Synch 64 (Figure 1). Also shown in Figure 1 is the Select Synch system that requires more heat checking that the other two systems. The pregnancy rates to these systems have been over 50% in postpartum lactating cows (Table 1).

These systems offer the advantage of no heat detection (OV-Synch) or limited heat detection (CO-Synch 64). In addition, they require only about 10 days from start to finish. All systems use a100ug injection of GnRH, which is commonly known as Cystorelin", Factrel" and Fertagyl". The PGF injection indicated in the diagram is either Lutalyse" or Estrumate". With Ov-Synch, all cows are bred at the same time 16 to 18 hours after the second GnRH injection. For maximum pregnancy rates, cows on CO-synch should be heat checked during the time between injection of PGF and mass breeding with injection of GnRH at 64 hours after PGF.

All the drugs for these systems must be obtained from your veterinarian. The cost of these systems is $8-$15 per cow depending on the system you use. Cost is also a function of the number of cows you will synchronize. The more cows, the lower the cost because of volume drug discounts. It may pay to shop around because some veterinarians do more reproductive work than others. Those that do considerable reproductive work may have a better price.

Table 1. Average AI pregnancy rate using different estrus synchronization systems (Virginia Trials)

SyncroMate-BSelect-SynchCO-Synch 64Ov-Synch
26/46 6/1427/49
44/93 (47.3%)36/66 (59.1%)125/244 (51.2%)116/211 (55.0%)

Ov-synch and CO-synch allow you to plan when cows are going to be bred. This allows you to schedule around your other on-farm or off-farm tasks. In addition, it is much easier to hire a technician if he can come to your farm and breed most, if not all, your cows in one trip. Select Synch works well but requires more heat checking, and you will be breeding cows over several days.

The above systems are not generally recommended for heifers. The MGA-prostaglandin system with heat checking is the best system for heifers. Contact your county agent for details.

Keys to making synchronization work

Although these new systems work well, they do not replace other aspects of good management. First, you must be committed to the system and doing things right and on time. Since these systems require 3 to 4 trips through the chute, they also add labor. An easy trick to cut down on the labor associated with these systems is to feed the cows some corn in a large pen or corral attached to your working chute. If you feed them everyday during the synchronization period, they will be easy to get up and put through the chute.

Next, cows need to be in body condition 5, 6 or 7 (good flesh). Thin cows will not respond well to the synchronization and will have poor AI pregnancy rates. Also, cows should be at least 30 to 40 after calving at the start of the injections. Cows can be given the injections as early as 2 weeks after calving but pregnancy rates to AI are likely to be low. However, these synchronization systems will "jump start" some late calving cows and they will breed earlier to the clean-up bull.

Make sure you get the best AI technician available. If you have just learned AI you may want to have the technician present to help you breed cows the first time. Don't let your pride interfere with getting high pregnancy rates. Keep everything very clean and follow all the proper semen handling practice you were taught.

Finally, always work the cows in a calm manner. Dogs, 4-wheelers, hot shots and other methods that get cows nervous don't need to be around the breeding chute. Commercial or homemade breeding boxes are a plus as well.

Good luck with your AI. If you have any questions, contact your animal science extension agent, your breeding service representative or me.

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