All bulls are not created equal. That simple truth, says Roger Ellis, Colorado State University Extension veterinarian, has created management considerations for cattlemen ever since the first rancher tried to manipulate the reproductive process in his cattle.

In short, he says, some bulls are high performers and some are slackers. Unfortunately, even today, with all the advanced management practices available to help you gain efficiency in your breeding program, there still isn't a good way to tell the difference.

And that difference is significant. Research shows that 20-40% of beef bulls can be sub-fertile or inefficient breeders. In research that Ellis conducted at the U.S. Meat Animal Research Center in Clay Center, NE, he found 40% of the bulls in a multi-sire breeding program sired 73% of the calves.

Breeding soundness exam

Four things are necessary for a bull to be a successful breeder, Ellis says. They are:

  1. Physical capability and soundness.

  2. Libido or the innate ability to mate, plus the acquired skill to do so effectively.

  3. Testicular development and health to produce sufficient sperm and testosterone.

  4. Sufficient healthy sperm to effectively fertilize the embryo and sustain its survivability.

A breeding soundness exam (BSE) can determine three of those four factors. But it's the X factor of the bull's libido — his desire to be an efficient breeder — that ultimately determines his individual success and, therefore, the overall success and efficiency of your breeding program.

That's not to say a BSE isn't worthwhile. It is, Ellis says, and should be routinely done.

“All in all, the bull breeding soundness evaluation, when properly performed and interpreted, provides a highly useful management tool and serves to reduce the risk of potential sub-fertility in herd bulls,” he says. In fact, it's generally accepted that about 10-20% of the bulls in any herd group won't pass a BSE.

You need to identify and cull those sub-fertile bulls. But that still doesn't fully guarantee your bull battery will get all the cows bred early in the breeding season. “Unfortunately, sexual behavior is not related to any of the components of the BSE,” Ellis says.

There is a way to evaluate libido in bulls, but it's not widely used. “The procedures are time-consuming, incur risks for animals and humans, require facilities and restrained females, and need standard and consistent application and sound interpretation. Therefore, they are generally found unfeasible and impractical to perform under field conditions,” Ellis says.

So what can you do? In lieu of a structured serving capacity/libido test, producers can apply management practices that will often detect these issues, he says. “Test-mating of bulls, particularly virgin yearling and two-year-old bulls, will allow observation for faults. A pre-breeding ‘sex education' period for young, inexperienced bulls has been suggested to allow for mating experience, tempering juvenile social behavior and observation for bulls with weak sexual behavior tendencies.”

However, the foremost management recommendation Ellis can give is simply to watch all your bulls regularly through the breeding season. If they're injured, which he says is the most common cause of early removal of bulls from the breeding herd, they need to be replaced. If they're just worn out, they need rest.

“A lot of times, we can give bulls a short rest period, and with a fresh stimulus of new estrus females, they'll come back around,” he says. “If they're physically exhausted, they're just going to need rest for a period of time. Oftentimes, rotation of fresh bulls into the herd to replace these exhausted bulls is necessary.”

Beyond libido and the elements identified in a BSE, other factors can affect a bull's performance. These include nutrition, environment and management. While management considerations are numerous, one aspect to consider is the social structure of the herd.

“Under natural mating conditions, the social ranking of bulls within the herd hierarchy can influence sexual activity and reproductive performance,” Ellis says. Older bulls tend to be more dominant. Dominance effects on herd fertility may be greatest at lower bull-to-female ratios, he adds.

The effects of hierarchy and dominance occur most frequently when older and younger bulls are run together in the same breeding pasture. To offset that, he recommends bull groups be relatively homogeneous for age, size and breed type. General recommendations to minimize the effects of social dominance in multi-sire breeding groups include:

  • Yearling bulls should not be included with older bulls.

  • Young bulls (2- to 3-year-olds) should be the core bull breeding groups.

  • Mixed-age, multi-sire groups should be utilized under high mating loads to avoid dominance effects during the early breeding season.

  • Bull rotations with aged bulls can be used early in the breeding season followed by young bull groups later in the breeding season.

Yearling bull management

Beyond the items above, yearling bulls deserve some special management considerations, Ellis says. These include:

  • Select yearling bulls for early maturity, testicular growth, satisfactory semen quality and health. If a bull fails the BSE at 12 months, Ellis recommends retesting in 30 to 60 days. “There's a major study that shows about 50% of the bulls at 12 months of age will not meet all the qualifications to be called a satisfactory potential breeder. But by 14-15 months of age, we're looking at 18-20% of the bulls that do not.”

  • Properly develop young bulls nutritionally. Don't over-condition.

  • Give bulls an opportunity to exercise so they're physically fit.

  • Prepare young bulls for changes in environment and nutrition at least 30 days prior to breeding season.

  • Utilize accepted bull-to-female ratios for yearling bulls of 1:20 to 1:25, knowing that individuals may not meet these expectations under the right circumstances.

  • Offer limited breeding exposure (less than 45 days) to allow young bulls to remain healthy, regain condition and continue growth.

It is with expectation and hope that ranchers turn bulls out for the breeding season every year — expectation that they'll breed the majority of the females early in the breeding season and a hope that they actually do. Bringing the expectation and the hope closer together is possible. The key, Ellis says, is constant vigil and observation of bull activity, health and viability.