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The Cow-Calf Manager:
Jump Start Your Cows for the Breeding Season

Livestock Update, December 1999

John Hall, Extension Animal Scientist, Beef, Virginia Tech

As I travel around Virginia this fall, I can see the improvement the fall rains made in some herds. Especially fall calving herds are looking better. Unfortunately, as much improvement as I've seen, we still have a long way to go in many herds. At a recent stock cow sale in the area, many of the cows I saw were body condition score 3. Most of these cows were spring calvers, but a few were fall calvers. For the past few months, I have talked about the impact of nutrition and body condition on rebreeding success. Now we need to consider some other options to "Jump Start" cows.

Jump Starting is when we use management procedures to start cows cycling that have not had any heats since calving. There are several different options for jump starting from hormones to animal movement and exposure. Jump Starting is especially important for young cows (2- and 3-year-olds) and thin cows (BCS < 4) because these cows will have an extended anestrus period (time without heats or estrous cycles).

Progestins. Progestins are compounds like MGA and norgestomet. The products act like progesterone, a hormone, that the cow normally produces during the estrous cycle and pregnancy. Progesterone normally increases before the first cycle after calving. It appears to get the brain and the rest of the reproductive system primed for starting new cycles.

MGA and norgestomet have been used for years to synchronize estrus in cows and heifers. A 7- to 14-day treatment of cows with either of these compounds will Jump Start cows. Cows should normally be a minimum of 35 to 40 days postpartum (since calving) to respond to this treatment.

Norgestomet is better known as the implant from the SyncroMate -B® system. Unfortunately, SyncroMate -B® is no longer available due to a failure of the company to file some routine paperwork with FDA. Veterinarians and other dealers can still sell their existing supplies, but the company will not be making anymore for awhile. So MGA is our only option until the EZ-Breed® CIDR becomes available in the next year or two.

GnRH. Cystorelin®, Factrel®, and Fertagyl® are all GnRH compounds that we currently use in the Select-Synch, Co-Synch and Ov-Synch estrus synchronization systems. Using any of these synchronization systems will Jump Start some cows. Ov-Synch works best followed by Co-Synch and Select-Synch. The GnRH causes a follicle to ovulate and produce progesterone naturally to kick-over the reproductive system.

Bull Exposure. Research from Kansas demonstrated that allowing cows to have access to bulls before the breeding season causes them to start cycling sooner (Figure 1.). However, this means that the bulls have to be vasectomized or their penis surgically altered so that they cannot breed cows. I knew a producer in South Dakota that chained mud flaps around the intact bulls' middle so they couldn't breed the cows! But ya gotta watch those mud flaps to make sure they stay in place.

Bull exposure works best for young cows. Also, the bulls must be "new" to the cows. In other words, the bulls need to have been away from the cows to make it work. Running bulls year 'round doesn't do any good. Another reason for a controlled breeding season.

Calf Removal. Separating cows and calves for 48 hours before the start of the breeding season is a proven method for Jump Starting cows. However, it is very labor intensive. To make the procedure work the best, calves should be out of sight and hearing of cows. Realistically, if they are out of sight of the cows, it will work. Calves need to have shelter, hay and clean water during calf removal. A dry area that is not too dusty is important.

With calf removal, we are removing the nutritional and psychological demands on the cow that inhibit cycling. After 48 hours, the reproductive hormones from her brain are increasing and the system is starting to turnover.

Jump Starting cows can be a hassle, but it is better than open cows. A combination of progestins and bull exposure or calf removal is probably the most effective.

Figure 1.

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