Breeding soundness exams can uncover problems with just-purchased young bulls and older bulls that have sired calf crops.
By: Ellen Crawford, NDSU Extension Service
Bull breeding soundness exams offer producers the opportunity to identify bulls with very low probabilities of siring calves and remove them from the breeding herd.
“Because the No. 1 determinant of profit potential in a beef cow-calf operation is the birth of a live calf, turning out infertile bulls can have a tremendous impact on profitability,” says Carl Dahlen, North Dakota State University Extension Service beef cattle specialist. “Breeding soundness exams can uncover potential problems with young bulls that were just purchased and older bulls that have already sired calf crops.”
However, less than 20 percent of producers in the U.S. perform breeding soundness exams (BSE) on their bulls prior to spring turnout, according to the National Animal Health Monitoring Survey.
Breeding soundness exams include an 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 to the rigors of the breeding season, compared with bulls with structural problems,” NDSU Extension veterinarian and livestock stewardship specialist Gerald Stokka says.
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. Bulls will lose body condition during a breeding season, so they must enter the season with adequate condition.
Vision also is an important part of the breeding season for bulls. Seeing the mounting behavior of cows in heat helps the bull identify, from across the pasture, which cows are ready to breed.
An evaluation of the reproductive organs is another important part of the BSE. That consists of evaluating the penis, testicles, prostate and other internal glands/structures. These organs need to be free of injuries or defects for a bull to breed cows.
Scrotal circumference is 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. For example, a bull that is less than 15 months old should have a circumference of at least 30 centimeters (cm), whereas a bull more than 24 months old should have a scrotal circumference of at least 34 cm. Bulls with inadequate scrotal circumference often are retested at a later date.
A sample of semen is evaluated for motility, morphology and concentration. Motility is the movement of sperm. Ideally, the examiner will see a rapid swirling movement in the sample. If sperm are not moving in a synchronized manner, they may not be able to navigate through the female reproductive tract to the fertilization site.
If less than 30 percent of sperm has proper motility, the bull is not recommended for breeding, whereas a bull with greater than 70 percent proper motility receives a very good rating for the motility portion of the BSE.
Morphology is an evaluation of the sperm’s structure. Ideally, the sperm will have the proper shaped head and tail. Common defects include tapered or detached heads and folded or coiled tails. Sperm that has the incorrect structure will not result in successful fertilization. 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,” Dahlen says. “Injuries during the nonbreeding months, as well as effects of extreme cold weather and frostbite, can render once-fertile bulls infertile.”
The process of making sperm, spermatogenesis, takes 60 days, but frostbite or other injuries that occur in March may be lingering in May and could affect the sperm development.
Dahlen advises performing BSEs close to the time of breeding to ensure that bulls have recovered from winter injuries. However, the tests should be done far enough in advance of turnout so producers have time to find new bulls if the BSE indicates fertility problems.
“An important indicator of breeding season success is stocking rate, or how many cows a bulls is required to breed in a breeding season,” Stokka says. “The nationwide average stocking rate is 25 cows per mature bull, or 15 cows per yearling bull. Stocking rates of up to 50 cows per bull are used in some systems, but high stocking rates may lead to cows not becoming pregnant on their first heat of the breeding season and subsequently calving late the following year.”
The BSE does not evaluate libido, or willingness to breed.
“This is very important to keep in mind, especially when using young or virgin bulls,” Dahlen 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.”