Factors That Affect The Breeding Ability Of Bulls

Here's a rundown on factors that affect the breeding ability of bulls.A breeding soundness examination (BSE) is the best place to start.

Heather Smith Thomas

March 25, 2011

10 Min Read
Factors That Affect The Breeding Ability Of Bulls

Not all bulls are created equal. So how do you maximize your chances of putting a powerhouse rather than just a pretty boy to work in the breeding pasture?

Many factors play a role in a bull’s fertility and breeding ability, including semen quality, reproductive tract soundness, limb structure and libido (desire to breed cows). Most of these can be determined with a breeding soundness examination (BSE), says Ram Kasimanickam, a DVM in Washington State University’s Department of Veterinary Clinical Sciences.

But, interestingly, Kasimanickam adds that a reader survey reported in BEEF magazine (February 2010) showed that only 37.2% of bull buyers considered a BSE important when selecting a bull. He advises producers to make sure every bull is BSE-certified before putting him out with cows.

A basic BSE evaluates five factors:

• Physical soundness – feet, legs, eyes, etc.,
• Reproductive tract soundness,
• A minimum requirement in scrotal circumference,
• A minimum percentage of normal sperm cells,
• Acceptable motility in the sperm.

Passing the physical

Mike Sanderson, Kansas State University professor of epidemiology and beef production, explains that testicles are palpated during a BSE exam to make sure they feel normal and can move freely in the scrotum.

“We palpate internal reproductive organs and make sure the penis extends and there’s nothing wrong with it. We also palpate to make sure there are no hematomas, which can cause adhesions that prevent the bull from extending the penis. If the injury has completely healed, the penis is able to extend and everything seems fine, we don’t worry about an old injury. But we make sure it can extend far enough that we know the bull can breed,” he says.

Scrotal circumference is measured because it’s an important indication of sperm production capacity, and may determine how many cows he can potentially settle, Sanderson says.

“If it’s a bull we’ve tested multiple years, we’ll check to see if his scrotal size has changed. If it declines, it may be a sign he’s declining in fertility. Of course, scrotal size can be influenced by how fat the bull is, but if we’ve kept records we can look back to see if there’s a change in his condition. If he’s a little smaller this year with a lower body condition score (BCS) and if his semen still looks good, he’s probably okay. We need to weigh all the factors,” Sanderson says.

Semen motility, or how well the sperm swim, as well as the percentage of normal sperm cells are monitored in a BSE. Abnormalities are recorded. While these can be difficult to interpret, these tests sometimes provide clues in the event of a problem, about whether it’s a new condition, what might have happened in the past, and how likely he is to recover, Sanderson says.

“We also check feet, legs and eyes. Vision is important for a bull to identify sexually active groupings of cattle. A valuable bull with a vision problem could be used in a small pasture with a few cows, but would not do well in a large pasture,” he says.

Dee Whittier, Virginia Tech professor of large animal clinical sciences, recommends a bull undergo a BSE every year. He points to research conducted at the Western College of Veterinary Medicine in Saskatchewan, Canada, where researchers examined all the facility’s BSE data and found a similar failure rate among bulls in all groups. That flies against the popular perception that it’s more important to BSE test young and old bulls because middle-aged bulls don’t typically have problems.

And, Whittier adds, even though a bull might pass the test today, he may not be okay a month down the road. “Bulls can get sick, or become injured or lame. The breeding season is a stressful time,” he says.

Watch for libido

A BSE doesn’t assess libido, but it’s just as important as fertility, the specialists say. After all, a fertile, sound bull won’t sire any calves if he doesn’t actually breed cows. The problem is that libido is difficult to measure in a test setting. That puts the responsibility onto the producer to monitor breeding groups to ensure each bull is doing his job, Whittier says.

While young, inexperienced bulls need to be closely watched, older bulls can suffer libido problems, too. An older, arthritic bull may find it painful to mount cows and an overweight bull can become lazy.
Sanderson recommends producers assess a bull’s ability and desire to mount a cow. If the bull has poor leg structure or exhibits arthritis or any kind of lameness that hampers mounting, he may not breed. In addition, a lame bull may lie down a lot, which makes thermo-regulation of the testes more difficult, Sanderson says. That can affect semen quality.

Body condition

Weight and condition are important determinants in whether a bull will be a good breeder. Proper fitness is necessary to deliver the athleticism and endurance needed to cover a large territory and breed a lot of cows.

“For a long time, I told producers they needed to have bulls in abundant flesh because they’d lose weight during breeding season and needed some reserve. Then I saw the results of a study in Canada involving some large community breeding pastures,” Whittier says.
That work by Glenn Coulter ultrasound-measured the backfat of a group of bulls on a community pasture. The bulls, the cows they were mated to, and their resulting calves were then all blood-typed to determine parentage.

“I would have predicted that really thin bulls would breed fewer cows, the really fat bulls wouldn’t breed very many, and that you’d want bulls to be in the middle,” Whittier says. “It turned out that those with zero backfat bred the most cows.”

A fat bull isn’t as athletically fit and more likely to hurt himself, just like an overweight, out-of-shape human who tries to exercise, he adds. He’s also more apt to be lazy.

“A BCS of 5 (with 1 being emaciated and 9 obese) is fine for a bull. A BCS 5 bull may not be pretty but he’ll settle more cows than a fat bull. It’s crucial that these bulls not be overly fat,” Whittier says.

Special considerations must be made for yearling bulls, however. A yearling bull that’s still growing may lose too much weight during his first breeding season, Whittier says. That’s why a yearling bull should be given fewer cows to breed or shorter turnout times, and be removed from the cows before he draws down too far in body condition.

Sidebar: Breeding injuries

While any bull can suffer a broken penis, torn sheath and other reproductive-tract injuries, some seem more prone to injury than others. There’s a correlation between being polled and having a looser sheath, for instance; horned bulls tend to have fewer injuries.

“Most bulls in our state are polled. When we went to polled bulls, we found a connection between polledness and the strength and development of the retractor-prepucial muscles. When these bulls relax, they prolapse the prepuce,” says Virginia Tech’s Dee Whittier. The professor of large animal clinical sciences says such prolapsed tissue can be injured when bulls fight or chase cows through the brush. “Constant vigilance is important to check for injuries, and remove injured bulls as soon as possible. The more quickly he can be pulled from the cows, the less damage there will be and a better chance for recovery,” Whittier says.

Any injury to the penis or prepuce usually puts that bull on the sidelines for the rest of that breeding season, he adds.

“These injuries often require extensive surgery or treatment in a clinic where the injury can be constantly cleaned and treated with drugs to reduce swelling and inflammation. Even then, the bull often ends up with scarring and is unable to extend the penis and complete the act of breeding,” Whittier explains.

Sidebar: Monitor your bulls

If you continually monitor bulls’ breeding behavior, you’ll know if a bull is injured and needs to be replaced immediately. But, you also need to know if certain dominant bulls are preventing others from breeding cows.

“If a bull becomes injured, he needs to be removed immediately,” says Virginia Tech’s Dee Whittier. “An injured dominant bull will continue to intimidate other bulls even if he can’t breed cows himself.”

And, some bulls would rather fight than breed. In a small pasture with only a few bulls, make sure the bulls are compatible. One old-time rancher recommends using either one or three bulls, rather than two, especially if the two bulls are evenly matched and always sparring. With three bulls, his reasoning goes, one might be able to breed the cow while the other two are fighting.

If you have just one bull in a breeding pasture, make sure he’s doing the job. If not, a little competition may spur a complacent bull to become a more aggressive breeder.

It’s also important to monitor bulls off-season – to know if any get sick or develop lameness. A fever, for instance, could affect his future fertility.

“It helps to know these things when the bull comes up for his BSE,” Sanderson says. “If there’s something wrong, and we have a good history, we might know when the bull had a fever. This information can be very helpful, not just for the veterinarian’s prognosis, but for the producer to know if the bull will recover by breeding season or needs to find another bull.”

Sidebar: Notes on yearlings

Young bulls have their own considerations. For instance, an inexperienced bull may spend all his time breeding one cow, whereas an older bull may breed each cow once and move to the next.

“Another problem when using yearlings as cleanup bulls in synchronized artificial insemination programs is that the cows that don’t settle all come in heat again at the same time. That can be more than a yearling bull can handle,” says Dee Whittier, Virginia Tech professor of large animal clinical sciences.

“We try to find ways to break in yearling bulls other than after a synchronized estrus, such as using them later in the breeding season to get some experience with a few cows.

“Producers spend a lot of money for new bulls and want a big crop of calves from them. But it’s even more expensive to end up with a bunch of open cows, so it’s important to have a modest number of cows for the yearling bulls’ first season,” Whittier says.

Whittier adds that yearlings are often developed in bull test settings; on average, they tend to be fat with a high rate of abnormal sperm cell development.

“These bulls grow fast, and may weigh 1,200-1,400 lbs., and a person might think they are ready to go, but they’re still young. It’s important to not expect or trust them too much. If cows are coming back in heat in significant numbers after 21 days, you need to make changes. Yearling bulls can easily let you down and you end up with too many open cows,” he says.

Sidebar: Weather, illness & diet

Weather, illness and diet are other factors to consider.

Optimum sperm production and quality depend on testicles being a few degrees cooler than body temperature. A bull must be able to lower his testicles in hot weather to cool them, and pull them closer to the body for warmth in winter. Scrotal frostbite can result in scar tissue that prevents the bull from raising and lowering his testicles, which can render him infertile.

Hot weather also can be detrimental to fertility, as can a high fever. Summer heat can render a bull temporarily infertile, while sperm formed during a fever will be abnormal; and infertility will follow for about 60 days following the fever.

“Fescue is our major grass in Virginia,” says Virginia Tech’s Dee Whittier. “The toxin in fescue inhibits cattle’s ability to shunt blood to the outside of the body to get rid of heat.” So it’s harder for the animal to regulate its temperature, and there’s more risk for heat stress.

“Cows suffering heat stress may not become pregnant (or may lose the embryo) but bulls are also adversely affected. We recommend producers introduce clover into fescue pastures, and have a fertilization program that doesn’t stimulate fescue to outcompete the other plants,” he says. It’s such a problem that spring calving has largely been abandoned in half the state of Virginia, he adds.

Subscribe to Our Newsletters
BEEF Magazine is the source for beef production, management and market news.

You May Also Like