Schedule Bull Breeding Soundness Exams Prior to Turnout
Carl Dahlen, NDSU Extension Beef Cattle Specialist
Not all bulls are able to breed cows successfully, and not all bulls that breed cows have semen that can result in successful fertilization and pregnancy. If a bull can’t fertilize cows and you turn him out to breed, you likely will have a lot of nonpregnant cows at the end of the year.
Breeding soundness exams can uncover potential problems with young bulls that were just purchased and older bulls that already have sired calf crops. However, less than 20 percent of U.S. producers perform breeding soundness exams on their bulls prior to spring turnout.
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 under the rigors of the breeding season than bulls with structural problems. Structural problems of the 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.
Seeing the mounting behavior of cows in heat helps the bull identify who is ready to breed from across the pasture so bulls must have good vision.
The penis, testicles, prostate and other reproductive organs are evaluated to make sure they are free of injuries or defects that would prohibit a bull to breed cows successfully.
Scrotal circumference is heavily scrutinized in young bulls because it is 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 an inadequate scrotal circumference often are taken out of production sales or sold at discounted rates, with their inadequate scrotal circumference mentioned at sale time.
A sample of semen is evaluated for motility, morphology and concentration.
Motility is the movement of sperm, and, ideally, a sample will have a rapid swirling movement. If sperm are not moving in a synchronized manner (think synchronized swimming), they may not be able to swim successfully through the female reproductive tract to the site of fertilization.
Morphology is an evaluation of the structure of the sperm. Ideally, the sperm will have heads and tails of proper shape. A high proportion of sperm that has incorrect structure will not result in successful fertilization.
Just because a bull sired calves last year does not mean he can do it again this year. 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, so frostbite or other injuries that occur in March may be lingering in May.
Perform breeding soundness exams close to the time of breeding to ensure recovery from winter injuries but enough time in advance of turnout to find new bulls if the exam finds fertility problems.
Considerations beyond a breeding soundness exam
- Stocking rate (number of cows a bull is required to breed): 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.
- Libido (willingness to breed): Can be determined only when bulls are on pastures or in pens with females in heat. Bulls may have all of the qualifications to pass the breeding soundness exam, 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.