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Breeding soundness exams provide crucial information for breeding season success

by Wyoming Livestock Roundup

Bulls are a big investment and their ability to breed cows is crucial to next year’s calf crop. Many factors play a role in fertility and breeding ability, so it’s important to make sure every bull has a breeding soundness examination (BSE) before being placed with cows. 

Even if a bull was fertile last year and sired many calves, there may be a problem this year producers are not aware of.  

Dr. Robert Larson, a Kansas State University Beef Cattle Institute professor, says an annual BSE for each bull is important for several reasons.   

BSE overview 

“When we run into situations where bulls are not successful breeders, this can have tremendous negative impact on breed-up for producers,” Larson notes. “If one female is sub-fertile, it hurts the producer a little, but if one bull is sub-fertile it can hurt a lot.”   

This means more open or late-calving cows, impacting the marketability of calves and producer schedules. 

“Male fertility is important for a successful breeding season, and a BSE is an important part of managing bulls,” Larson continues. “Some people think it’s just a semen evaluation, but many mature bulls fail for other reasons – they may have issues with lameness, injuries and other problems limiting their ability or willingness to mate.  A good physical examination is crucial, giving particular attention to feet, legs and structural soundness.” 

A bull in pain due to lameness may be unable or unwilling to breed cows. A thorough physical exam is important, along with examining the reproductive organs which could potentially create difficulty for mating, as well as a semen evaluation.  

Scrotal circumference 

While checking scrotum and testicles, scrotal circumference is measured.   

“For yearlings, scrotal circumference is a good indication of where they are in their maturity and how they compare to other bulls of similar age,” Larson explains. “For adult bulls, I don’t expect their scrotal size to continue growing, but I check records from the year before, particularly if there is a problem in semen evaluation.” 

Larson looks at previous year’s records to see if there is any change. Sometimes, a larger scrotal circumference will indicate a problem, but if scrotal circumference is smaller than it was before, this is evidence of something detrimental to reproduction.  

“We use the same tool – scrotal circumference – for yearlings and older bulls, but interpret it a bit differently,” he continues. “The Society for Theriogenology, comprised of veterinarians focusing on reproduction, sets the minimum at 30 centimeters for yearling bulls.” 

Larson adds, “Most breeders put more selection pressure on bulls of this age and consider the minimum to be 32 centimeters. This is the most common standard, to make sure these young bulls are actually reaching puberty and ready to breed.” 

“The scrotal circumference procedure during a BSE for yearlings is the same as for mature bulls, but there is a need to figure out if bulls have reached puberty or have enough sexual maturity to be fertile,” Larson explains. “It’s not that bulls can never be fertile, but whether they can be fertile in the time frame a producer needs them to be.” 

Mature bulls 

“Often we are asking young bulls to go into their first breeding season soon after they reach puberty, so if they are a bit slow, they may not work well this year,” Larson says. “By contrast, if a mature bull was a successful breeder in previous years, we are looking for signs of degeneration, lameness or problems due to injuries.” 

He continues, “I am looking for any problems young bulls might have in becoming fertile. With older bulls, I am looking for indications they might be losing their fertility for some reason.” 

It is important to examine mature bulls because various things can happen in a year’s time which might affect breeding ability. Bulls may have suffered injury or diseases impacting fertility.   

“We want to make sure bulls are ready to go for the current year,” says Larson. “A tough winter can be hard on bulls. Some have lost weight or suffered scrotal frostbite.” 

He explains, “There tends to be more failure of bulls following a difficult winter than a mild winter. In fact, veterinarians will often always fail some bulls which were successful in the previous breeding season after a tough winter.”  

It is important to examine all bulls before breeding season. Although it is disappointing for producers to have a good bull fail a BSE, it is even more disappointing to not check the bull’s breeding soundness and find out during pregnancy checking the bull didn’t do his job.   

Successful bulls 

A bull must pass the entire exam to be considered sound for breeding. 

“Failure in any one part would indicate the bull is probably not going to be a successful breeder,” Larson shares. “Generally, sub-fertility is the case rather than infertility. It is rare to find a bull unable to get any cows pregnant, but producers need a bull to be able to get a lot of cows pregnant in a short time.” 

“Bulls only getting a low percentage of the cows pregnant are not good enough,” he adds. 

Injuries and illness can happen after breeding season begins. Even if the bull was fine at the time of his BSE, producers need to monitor bulls throughout the breeding season.   

As bulls travel around, breed cows and possibly fight other bulls, there are risks, and even if they start the breeding season sound, producers could run into issues.  

Ideally, producers should watch every bull mate to make sure he can do it. Some problems and injuries may not show up until the bull is trying to breed a cow and fails, and some bulls may mount the cow but not actually breed her.  

Close observation enables producers to notice a bull having problems, and this provides a chance to replace him before the breeding season is over. 

Heather Smith Thomas is a corresponding writer for the Wyoming Livestock Roundup. Send comments on this article to 

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