by Elizabeth Cronin, North Dakota State University

In a cow-calf operation, open cows bring disappointment on the day of pregnancy diagnosis. To ensure a bull is capable of breeding, North Dakota State University (NDSU) Extension specialists recommend bulls undergo a breeding soundness exam (sometimes referred to as a BSE) prior to the breeding season.

“Considering that 92% of cows and 76% of heifers in the country are only exposed to natural-service sires, bull health and fertility are crucial to the overall success of the beef herd.”
— Lacey Quail

“The role of bulls on cow-calf operations is to get cows pregnant,” says Lacey Quail, Extension livestock management specialist at the NDSU North Central Research Extension Center. “Considering that 92% of cows and 76% of heifers in the country are only exposed to natural-service sires, bull health and fertility are crucial to the overall success of the beef herd.”

A breeding soundness exam helps to ensure bulls are capable of fulfilling their role. Quail recommends all bulls be subjected to a breeding soundness exam each breeding season, whether they are a new purchase or a resident herd sire. Because sperm production is a continuous process and bull fertility can change over time, the breeding soundness exam should be performed close to the start of the breeding season. Ideal timing for the exam is 30-60 days prior to turnout. This time frame allows ranchers to source new bulls if a bull does not pass its exam.

A complete breeding soundness exam evaluates three categories:

1. physical soundness, including feet, hip and leg structure; body condition; vision; penis; and accessory sex organs;
2. scrotal circumference; and
3. semen characteristics, such as sperm cell motility and morphology.

Based on the results in each of these three categories, a veterinarian classifies the bull as satisfactory, unsatisfactory or deferred. A satisfactory breeder meets the minimum requirements in all categories and is free of physical problems. Bulls that do not meet the minimum requirements in at least one of those categories are unsatisfactory, or deferred for another evaluation at least 30 days later. Unsatisfactory breeders likely will not improve with time. But deferred bulls may benefit from treatment or additional time and may pass a breeding soundness exam in the future.

Why bulls fail the exam

There are a variety of reasons why a bull may not pass a breeding soundness exam. An injury or frostbite may have impaired the bull’s ability to produce healthy sperm; or feet, leg or hip issues may prevent the bull from mounting and breeding cows, despite having adequate numbers of morphologically normal and motile sperm cells. On the other hand, yearling bulls may not have reached sexual maturity, decreasing the likelihood of passing a breeding soundness exam. In all of those scenarios, a bull may not be capable of breeding cows.

Several options exist when a bull fails a breeding soundness exam. One obvious solution is to market bulls that do not pass the exam. This ensures that inadequate breeding sires are off the property. While marketing these bulls is often a necessary solution, particularly for unsatisfactory breeders, other factors may come into play.

“Market value, availability of additional bulls in your area, and affordability of a new bull that might fit your breeding program all contribute to the decision of whether to market a bull,” Quail says. “With these factors in mind, it is crucial that initial breeding soundness exams are performed early enough prior to the breeding season to allow for the worst-case scenario.”

What if a bull is deferred?

If a bull is deferred at the initial breeding soundness exam, marketing the bull may not be necessary. In this scenario, the veterinarian likely recommends that the bull be retested at a later date. This is often the case when a bull may need treatment and time to heal from a foot abscess, penile warts or an infection that resulted in too many white blood cells among sperm cells — all conditions that may improve with time.

Commonly, young bulls may fail their initial breeding soundness exam due to a decreased percentage of normal or motile sperm cells. While that may not sound promising, breed and age considerably affect when a bull reaches sexual maturity. Research has reported that nearly 50% of yearling bulls that failed an initial breeding soundness exam were later classified as satisfactory.

“If you have available feed resources, facilities, and time before the breeding season starts, keeping a yearling bull to be retested is often the best option,” Quail advises.

The good news is that spermatogenesis, the process of producing sperm cells, is a continuous process, and a single cycle takes about 60 days in bulls.

“A single breeding soundness exam is simply a snapshot of a bull’s fertility on that particular day. But it is the best and only tool we have to evaluate a bull’s fertility potential and, thus, his ability to get cows pregnant,” Quail explains. “By identifying bulls that fail a breeding soundness exam, we are keeping infertile and subfertile sires out of our herds, which is progress towards improved reproductive efficiency.”

Editor’s note: Elizabeth Cronin is an information specialist and interim director of agriculture communications for NDSU.