In Montana, springtime brings the happy sight of momma cows and calves. But as a producer, is there a way that you can help your herds to have higher yields? As it turns out, you can–by testing your bulls’ fertility.


Skelton Ranch Calves

What Happens During a Fertility Test

During a fertility test at Bridger Vet, which is also called a breed soundness exam, a bull will be brought into a chute, and a semen sample is obtained usually using an Electro-ejaculator. What follows is an explanation of the major portions of the exam.
Body condition–Once the bull is in the chute, the vet will look over its general body condition, checking for any injuries that may make him unable to mate. Bulls that are too fat, too thin, or those with leg problems, aged bulls, disease, or injury can affect their ability to breed successfully. By verifying a bull’s overall physical condition, your ensure that he is physically able to do his job.

Note: As a producer, it’s also a good idea for you to keep a weather eye on your bulls at pasture. Do they move well? Have you seen lameness or foot injuries? If so, be certain to talk to your veterinarian about what you have seen.

Scrotal measurements–As part of the exam, the vet will measure the bull’s scrotal circumference. Bulls with larger scrotal circumferences are more fertile and tend to produce more fertile offspring. This doesn’t mean that smaller bull won’t get a cow bred, but they likely won’t “settle” as many cows. Conversely, bulls that have an abnormally large scrotum are not necessarily more fertile.

Semen testing–Once the bull’s physical condition is assessed and the scrotal measurements are verified, the vet will manually palpate the bull and then use an electro-ejaculator to collect a semen sample. This sample is then viewed under a microscope to determine sperm motility and morphology. In order to pass a fertility test, the bull’s sperm must pass these metrics:

  • Motility–30% or more of the sperm cells must exhibit good forward motion, not spin or swim in a circle.
  • Morphology–70% or more of the sperm cells must be normal in order to be considered a sound, breeding bull. The vet is specifically looking to see that the sperm heads and tails are without deformities such as giant heads, twin head, or coiled tails. In order to pass, 70% of the sperm cells in the sample must be without deformity.

Morphological abnormalities of spermatozoa identified through examination of semen for quality

Note: If a bull fails a breeding soundness exam, there may be a temporary reason. It is often worth testing that bull again after 30 days, giving him time to recover.

Taking notes–The notes that a veterinarian takes during a fertility exam will include notations on breed, identification number, age, scrotal circumference, motility, morphology, and scoring of poor, good, very good, or excellent. She will also note body condition, any lameness, past or current trauma to penis area, age, and suggestions regarding herd management and replacement. Bulls are an asset, and the comment section of each exam can help you to remember what you talked about. You veterinarian wants you to be successful and profitable, and this section can help you to plan for the future.

Asking the Hard Questions

  • How many cows does the average bull service?–This depends on bull, whether or not the bull must compete to breed cows, how rough the country is, how good the pasture is, and if he failed his last exam. Libido is generally not part of a breeding soundness exam.
  • When should I have my bulls tested?–This depends on many factors including the bull’s breed, whether the bull is going to be sold, and so on, but spring is generally considered to be the best time. This way, if you do need to buy a bull, you can do so at spring bull sales. Depending on breed, some breeds mature more slowly, meaning that their fertility scores will differ when compared to other breeds of the same age. If you’re in the business of selling bulls, it is best to begin testing before the sale date. If you’re buying a bull, be certain that he has passed his breeding soundness exam and has tested negative for trichomoniasis. Some states require that all bulls be tested prior to sale out of state.
  • Does a bull’s age or maturity influence its fertility test?–Absolutely! When bulls younger than one year of age are tested, their testing scores will likely be questionable. This does not mean that the bulls are not quality stock, but just that they may not be ready to be turned out with the cows just yet as they have not matured sufficiently.
  • What percentage of bulls fail a fertility test?–Approximately 10% of bulls will not pass fertility tests after physical maturity is reached due to age, condition, or fertility issues.
  • How long should bull be kept around if it fails a fertility test?–If a bull fails two consecutive fertility tests, you should strongly consider selling that bull. Not only is  he likely a pasture ornament, he may be keeping other, younger bulls from servicing cows. He is a double liability.
  • What about trichomoniasis?–Trichomoniasis is a venereal disease found in the reproductive tracts of affected cattle. If contracted, it can be a devastating disease as it results in low birth weights, low fertility rates, and diminished calf crops. It has not been a problem in Montana in recent years, although the Montana Department of Livestock did report a case in Yellowstone County in 2016.

Now that you understand what bull testing is, let’s do the numbers.

Average Annual Cost of a Bull

As this is Montana, let’s assume that a bull can be pastured for six months of the year and fed hay for the other six months. The average cost of a feeding a bull for one year breaks down like this.


As you can see, the cost of infertility can be quite high in feed costs alone.

Future Profit Losses Due to Bull Infertility

Let’s say that you have a small herd of cows, about 20-25 head, along with one bull. If that bull is partially fertile, that might result with about 25% of a producer’s herd not being bred for the upcoming year. Each calf’s current market value at weaning is about $1,000, so the loss would be $5,000-$7,500 on unborn calves alone. This does not include the annual cost of feeding and maintaining dry cows for a year. If a bull is completely infertile, that would be a total loss for next year’s calves, the full $20,000-$25,000.

If you have a slightly larger herd of 40-50 cows with two bulls, one of whom is infertile and the other is fertile. That second, fertile bull may pick up some of the work. However, if 10%-20% of the herd is not bred, that could still mean a $5,000-$10,000 loss in potential income or the following year.

When you look at the numbers, it’s easy to see why fertility testing is not only good for your breeding program but for your pocketbook. At Bridger Vet, we encourage producers to test their bulls annually to ensure that they are producing revenue rather than simply eating your profits.