NDSU Extension - Mercer County


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Bulls May Fail Breeding Soundness Exams

bull semen evaluation (BSE) exams, bull breeding

Submitted by Craig Askim, Extension Agent/Agriculture and Natural Resources

The cold weather conditions in March/April may cause problems for livestock producers concerning bull semen levels. Producers are strongly encouraged to have bull tested before turning them out for the breeding season.

Some cattle producers may be frustrated with breeding soundness exams in bulls this spring."Normally, warmer spring temperatures increase the pass rate of bull semen evaluation (BSE) exams," says Gerald Stokka, North Dakota State University Extension veterinarian and livestock stewardship specialist. "However, the record cold in April can produce less than satisfactory results some six to eight weeks later."

The sperm development cycle in bulls is approximately 60 days long. Depending on the nature of the problem affecting the testes, such as heat, freezing temperatures, stress or infectious diseases, and the severity and length of the problem, semen quality will vary. This means severe frostbite or other injuries that occur in March still may be lingering in May and June.

Bull breeding soundness exams offer the opportunity to identify bulls that have very low probabilities of siring calves and remove them from the breeding herd. Breeding soundness exams include examination of the bulls' physical structure, reproductive organs and semen.

"The physical examination is important because bulls with proper structure are more likely to hold up during the rigors of breeding season, compared with bulls with structural problems," says Lisa Pederson, NDSU Extension beef quality specialist.

Structural problems with feet and legs or movement in general are a big issue because bulls are asked to cover a lot of ground and need to be free of physical problems to breed cows successfully, the specialists note. Bulls will lose body condition during a breeding season, so they must enter the breeding season with adequate condition.

Evaluation of the reproductive organs is another important part of the breeding soundness examination. These organs need to be free of injuries or defects for a bull to breed cows successfully. Scrotal circumference is heavily scrutinized in young bulls because it serves as an indicator of semen volume. As young bulls grow, the standards for adequate scrotal circumference also increase. During a BSE, a sample of semen is evaluated for motility, morphology and concentration. A minimum of 70 percent of the sperm cells need correct morphology for a bull to pass a BSE.

"Just because a bull sired calves last year does not mean he can do it again this year," Pederson says. "Injuries during the nonbreeding months, as well as effects of extreme cold weather and frostbite, can render once-fertile bulls infertile."

She recommends producers perform breeding soundness exams close to the time of breeding to ensure the bulls have recovered from winter injuries but far enough in advance of turnout to find new bulls if the BSE identifies fertility problems.

An important indicator of breeding season success is the number of cows a bull is required to breed in a breeding season. The nationwide average is 25 cows per mature bull or 15 cows per yearling bull. Rates of up to 50 cows per bull are used in some systems, but high rates may lead to cows not becoming pregnant on their first heat of the breeding season and subsequently calving late the following year.

One factor the BSE does not evaluate is libido, or willingness to breed. "This is very important to keep in mind, especially when using young or virgin bulls," Stokka says. "Young bulls may have all of the qualifications to pass the BSE, but if they aren't actively breeding cows, producers must find a different option.  "Watch breeding activity closely because catching and correcting problems during the breeding season is much more profitable than waiting for open cows to calve," he adds.

Source: Gerald Stokka, 701-231-5082, gerald.stokka@ndsu.edu

Source: Lisa Pederson, 701-328-9720, lisa.pederson@ndsu.edu

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