Bull Breeding Soundness Evaluation

A bull breeding soundness evaluation is an exam conducted by veterinarians that includes a physical exam, semen evaluation, and an internal and external exam of the reproductive tract.

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THE SINGLE MOST IMPORTANT COMPONENT OF

a successful breeding program is using fertile bulls that have passed a bull breeding soundness evaluation (BSE). Each bull is expected to contribute to 20 to 50 pregnancies each year, while individual cows contribute to just one pregnancy per year. Having a BSE conducted on breeding bulls is crucial to a successful breeding program.

The BSE is an exam conducted by veterinarians that includes a physical exam, semen evaluation, and an internal and external exam of the reproductive tract. The BSE should be conducted 30 to 60 days prior to breeding to allow sufficient time to retest or replace bulls that fail the BSE. It is important to note that the bull’s sperm production cycle is approximately 60 days, and if illness, injury or other issues occur, this could negatively impact the BSE and breeding capability of the bull.

Figure 1. Reproductive Organs of a bull. (University of Wisconsin)

Physical Examination

The physical examination evaluates the bull’s physical ability to breed cows. Physical structure and body condition are extremely important factors in Montana due to the distance and terrain bulls may need to travel to breed cows. The physical exam identifies problems such as poor vision, bad teeth, and poor feet and leg structure.

Body condition, or flesh cover, varies by breed, age, physical demands of winter and the previous breeding season, and feed availability. Body condition should be adequate at the beginning of the breeding season. A good “rule of thumb” is that bulls should have enough fat cover at the beginning of the breeding season that their ribs are not visible but are felt. A thin bull may not have enough stamina to breed many cows in the timeframe allotted. However, a fat bull may not be able to travel extensive distances to breed. Sperm quality can also be negatively impacted in fat or thin bulls.

Bulls should have sound physical structure, which will improve mobility. Good feet and legs are needed to travel to the cows, breed, and travel to water and feed sources. Sore feet or stress on tendons and joints due to sickle hocks or post legs can reduce mobility and result in fewer cows being bred. Checking joints for swelling or injury can aid in identifying bulls that are not physically sound to breed. If hooves need to be trimmed, trim four to six weeks prior to turnout to ensure recovery prior to the breeding season.

Vision is an integral component of the BSE because bulls use sight to identify cows in estrus. Eyes should be clear and free of injury and disease, such as cancer eye and pinkeye.

Reproductive Tract Examination

A reproductive tract exam includes an external exam and an internal exam of the bull reproductive tract (Figure 1).

Internal Examination

The internal exam of the reproductive organs is completed rectally. These accessory sex organs produce the seminal fluid and include paired ampulla, seminal vesicles, prostate, and Cowpers glands. The ampulla are enlargements of the vas deferens where they join the urethra (common duct for both semen and urine). The seminal vesicles are glands that extend from the urethra and are lobular. Seminal vesiculitis is an infection of the seminal vesicles and causes the glands to become enlarged and lose their lobulation. Seminal vesiculitis results in swelling, poor sperm quality, and pus in the ejaculate. The prostate and Cowpers glands are located over the pelvis around and above the urethra.

External Examination

The external examination includes the testes, scrotum, epididymis, penis, and prepuce. The testes should be firm upon palpation. The condition of the scrotum should be evaluated to ensure there has been no injury or frostbite (often noticed by scabs on the bottom of the scrotum). Injury to the bottom of the scrotum can cause damage to the tail (cauda) of the epididymis, which will reduce sperm quality and availability.

The evaluation of the penis and prepuce requires the penis to be fully extended for evaluation. Both should be free of inflammation, adhesions, warts, abscesses, and deviations. The penis, when fully erect, should run parallel to the body.

Scrotal Circumference

Scrotal circumference (SC) is an important factor in a BSE because it is used to estimate the sperm producing ability of bulls. Scrotal circumference is measured with a scrotal tape around the largest part of the scrotum (Figure 2). Bulls with larger testicles produce more sperm and this trait is heritable to their male offspring. Additionally, bulls with larger testicles sire daughters with earlier age at puberty. The minimum age and SC measurements required for passing the BSE are provided in Table 1.

FIGURE 2. Diagram of measuring scrotal circumference. (Virginia Polytechnic Institute and State University)

Semen Evaluation

The most common method of collecting a semen sample is electroejaculation. There are two primary factors used in evaluating semen quality, sperm morphology and motility. Additional measures include ejaculate volume, sperm viability, and sperm concentration.

Sperm motility is evaluated as the percentage of sperm moving in a linear progressive manner (individual) or as gross motility (Table 2). Sperm motility can be a subjective measurement and may vary between veterinarians. A minimum rating needed to pass a BSE is fair, or greater than 30% linear progressive movement. Semen collected for freezing for AI generally has a minimum of 60% linear progressive motility or it is discarded.

Sperm morphology is evaluated on a stained slide by counting the percentage of sperm that are of normal form and structure. Morphology is evaluated on the percentage of normal cells, primary and secondary abnormalities, and other cells in each ejaculate. Primary abnormality examples that can occur are underdeveloped sperm, acrosome defect, narrow head, coiled tails, and accessory tails. Secondary abnormality examples are free normal heads, bent tails, and distal droplets. As one might expect, primary abnormalities are those known to be more detrimental to fertility and those not expected to improve over time. Other cells that can be seen in the ejaculate are white blood cells, red blood cells, and epithelial cells. Primary and secondary abnormality examples are illustrated in Figure 3.

FIGURE 3. Primary and secondary sperm abnormalities that may be observed in a breeding soundness exam (Dr. Bruce Eilts, Louisiana State University).

Classification

Based on these criteria, bulls are classified as satisfactory, unsatisfactory, or deferred. Bulls that meet the minimum requirements of the BSE will be classed as satisfactory potential breeders. Bulls that fail any of the minimum standards will be classed as classification deferred. If bulls are labeled as classification deferred, they should be tested again in two to six weeks, at the advice of a veterinarian. If older bulls fail subsequent tests, they will be classed as an unsatisfactory potential breeder. Younger bulls that are initially labeled as classification deferred may not have reached sexual maturity and may warrant retesting.

General Considerations

A BSE provides a snapshot of the bull’s current status as a potential breeder. It is really a better measure of infertility than fertility because it allows us to identify those bulls that are not fertile but if used in a breeding pasture, may be dominant enough that they prevent fertile bulls from settling cows. The BSE may aid in making breeding bull decisions, but it does not predict conception rates or actual fertility. A BSE also does not evaluate libido. Producers should monitor bulls when turned out for breeding to ensure that all bulls are actively breeding cows.

References

BIF. 2018. Guidelines for uniform beef improvement programs. 9th rev. ed. Beef Improvement Federation, Prairie, MS.

Whittier, W.D., and T. Bailey. 2009. Predicting bull fertility. Virginia Cooperative Extension. Publication 400-009.