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Calf crop depends on bull management in breeding season

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Assuming your bulls have passed a breeding soundness examination within the last 60 days, are carrying adequate condition (body condition score of 6 or higher), are structurally sound, and have been immunized and treated for parasites, they probably are ready to go to work. Your bulls may already be out earning their keep in your spring-calving herd. However, since so many things can go wrong during a 60 to 90 day breeding season, it is good management to observe them regularly after turn-out to make sure they are still willing and able to do their job.

I recommend making time, daily if possible, to watch each bull in action during the breeding season. A bull's interest in mating, his libido, should be assessed immediately. Obvious physical problems that may have arisen since turn-out can be detected and addressed, like lameness or injury. Another simple management practice is to record the tag numbers of the cows and the dates a bull services them, then find those cows in 18 to 23 days to make sure they are not coming back into heat. That, of course, would indicate he may have become infertile and you could address it in a timely manner.

Another concept is social ranking or dominance in herds where two or more bulls are turned out together. Research shows that dominant bull(s) will breed more cows compared to less dominant bulls, especially when older and younger bulls are used together. In one study, the dominant bull of a four-bull group sired 70.4 percent of the calves. The remaining three bulls, a 4-year-old, a 3-year-old and a 2-year-old sired 16.7 percent, 7.4 percent and 5.5 percent of the calves, respectively, in the first year of a five-year study. Age is usually the primary factor in determining dominance in a bull battery, up to a certain point. In one study, the dominant bull went from siring 70 percent of the calves at 10 years of age to 12 percent just two years later.

Using bulls that are roughly the same size and age can reduce the problem with dominance. Also, since dominant bulls work harder, they will lose condition quicker. Rotating these bulls out of the herd for a week or two of rest and added nutrition is one way to deal with this situation. While they are out of the herd, the less dominant bulls have more chances to work. Another approach is to start the breeding season with older bulls and replace them with the younger bulls later; still though, there will be dominance in each group.

Rotation can also be used to maximize the use of a bull battery made up entirely of young bulls. Glenn Selk, Ph.D., Oklahoma Cooperative Extension animal reproduction specialist, says that rotating them at a minimum of two weeks will allow for optimum reproductive performance and prevent young bulls from becoming too fatigued or lose condition too rapidly. If pasture and management capabilities allow, rotating young bulls once per week should slightly improve reproductive performance.

Bulls need to be managed all year, especially during the breeding season. Your next calf crop depends on it.

Clay Wright
Former Technical Consultation Manager