The Cow-Calf Manager, December 1998

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John B. Hall, Extension Animal Scientist, Beef, Animal and Poultry Sciences, Virginia Tech

Artificial insemination of cows is a powerful genetic tool that will improve quality and consistency of the calf-crop. In addition, it can enable groups of small producers to function like a large one as they pool calves from the same AI sire for marketing. An excellent example of this grouping strategy is the Buckingham Co. Cattlemen's Association who over the last three years have bred close to 2,000 cows to the same or similar AI sires. These cattlemen are then pooling their calves and marketing tractor trailer loads. Several other cattlemen's organizations across the state are trying similar programs. This Buckingham program is more complex than I have described it, but those who are interested in how they got started should contact extension agent Jim Myers or a member of the Buckingham Cattlemen's Association.

One of the primary factors in making an AI program work for beef cattle, especially producers with off-farm jobs, is estrous synchronization. With estrous synchronization, almost all cows will be AIed in one to three days. I have never been a big fan of timed insemination because conception rates are 15% to 20% lower than estrous synchronization with heat detection. However, the reality is that for producers with off-farm jobs it is difficult to do estrus detection and pull cows for breeding once every 12 hrs for 3 to 5 days. Timed AI also let's you hire an experienced technician at a reasonable cost because he only has to make one trip to the farm. So let's talk about timed AI systems that work for small or large producers in Virginia.

For cows the best systems are those that will induce cycling in non-cycling cows and result in a tight synchrony for timed AI. The top three systems that fit those criteria are Syncro-Mate B, Ov-Sync and Co-Sync.

This system consists of an injection of progesterone and estradiol on the same day cattle are implanted with Norgestomet, a progesterone analog. The implant remains in place for 9 days and then is removed on day 10. Cows are timed inseminated 48 to 52 hours after implant removal.

For example: Cows are implanted and injected on Monday, implants removed on the next Wednesday and inseminated on Friday. In studies done in Virginia, conception rates to timed AI run between 35% and 50%. Cost of Syncro-Mate B is between $6.50 and $7.50 per cow. It takes three trips through the chute to do the synchronization and breeding. Some cows have sub-fertile estrus and poor conception rates. In most cows conception rate is good. Implanting results in additional labor.

GnRH (cystorelin®, 100 ug) is injected on day 1 to luteinize/ovulate all follicles, PGF (lutalyse®, 25 mg) is given seven days later to regress CL and start new follicle growing. Second injection of GnRH is given 2 days after PGF and cows are time-bred 16 to 24 hrs later.

For example: Cows are given GnRH on Monday, PGF the next Monday, the second GnRH on Wednesday and bred on Thursday.

This system takes 4 trips through the chute and costs $9.00 to $12.00 per cow. Trials in Virginia indicate conception rates from 40% to 55%. It is generally recommended that cows that show heat between the PGF injection and the 2 GnRH injection be inseminated 12 hours after they show heat.

This system is similar to the Ov-Sync system except that breeding and the second injection of GnRH occur at the same time. GnRH (cystorelin®, 100 ug) is injected on day 1 to luteinize/ovulate all follicles, PGF (lutalyse®, 25 mg) is given seven days later to regress CL and start new follicle growing. Second injection of GnRH is given and cows inseminated 48 hrs after PGF.

For example: Cows are given GnRH on Monday, PGF the next Monday, the second GnRH and bred on Wednesday. This system takes 3 trips through the chute and costs $9.00 to $12.00 per cow. Trials in Virginia indicate conception rates from 35% to 50%. Recent experiments in Virginia and Colorado show there may be a 5% to 10% conception rate advantage to waiting until 64 hours after PGF to inject and inseminate. We will update you on this as the data is analyzed and more studies are conducted.

Of the systems mentioned in this article, only Syncro-Mate B seems to work well on heifers. There are a large variety of estrous synchronization systems that work well with estrus detection, and even some for use with natural service. If you are interested in these other systems contact you extension agent or me at (540) 231-9153.