Bull breeding soundness examinations
| Critter care |
By Sarah Eaton, DVM, DACT
A bull makes up 50% of a herd’s fertility. In the same way, a bull can be responsible for at least half, if not all, of a herd’s infertility. The presence of a subfertile or infertile bull within a herd can cost the producer immediately, since the bull and cows have to be fed while they are not producing, or the following spring by a late or reduced calf crop.
A breeding soundness examination (BSE), performed by a qualified veterinarian, helps the producer identify most bulls with low fertility to avoid adding them to a cow herd. There are three main parts to a bull BSE 1) Sex drive and mating ability; 2) Physical soundness; and 3) semen quality.
Sex drive and mating ability is based on observations by the producer and sometimes the veterinarian. The bull should be observed to make sure that he can identify a cow in heat, travel to her, mount the cow, and breed her. Some bulls have vision problems which prohibit them from seeing the cow in heat.
Other bulls have lameness and mounting issues. Finally, problems like a penile deviation may not be seen on the bull BSE but are visible when evaluating the bull in the field mounting cows. If a producer has concerns about a bull’s libido or his ability to mount and breed a cow then a serving capacity test may need to be performed.
The evaluation of physical soundness evaluates the bull’s expected ability to see and breed the cows. Emphasis is placed on the bull’s musculoskeletal system as a bull is expected to be able to travel long distances to detect and breed females in heat. The bull’s eyesight is also evaluated as bulls identify females in heat visually. The reproductive system, both internal and external, is evaluated as well to look for problems.
The contents and size of the scrotum is evaluated by palpation and measurement. Large scrotal sizes have been correlated with early puberty in the bull’s female offspring, which translates to earlier chances for heifers to be bred. The internal sex organs and accessory sex glands are evaluated by transrectal palpation to identify any signs of infection, inflammation, or damage to the reproductive tract that may inhibit sperm movement. In addition, physical defects that may be heritable are noted.
Finally, semen is collected, either by electroejaculation or transrectal massage. The semen is evaluated for volume, density, motility, and morphology (shape). To pass a bull BSE, the semen is expected to be above a certain density, with motility greater than 60%, and be at least 70% morphologically normal. Semen with these characteristics is expected to have normal fertility. Bulls with lower semen parameters may still be able to impregnate cows but with a lower success rate or it may take multiple breeding cycles.
Once a bull BSE has been performed the bull is characterized into 4 categories 1) Satisfactory; 2) Decision deferred; 3) Questionable; 4) Unsatisfactory. Satisfactory bulls are those who have met the minimum requirements for physical soundness and semen quality. Unsatisfactory bulls are those that are expected to have poor fertility in the cow herd in the upcoming season.
The decision deferred category is for pubertal bulls with poor semen quality that would be expected to improve with maturity or for mature bulls that have suffered from a recent disturbance in sperm production and are expected to make a complete recovery before the breeding season commences. Questionable bulls are those animals that could most likely get a cow pregnant but would have below normal pregnant rates or pass along an undesirable heritable trait such as a corkscrew claw.
The evaluation of bulls before entering the breeding herd allows the producer to cull those animals that will be non-producers. Approximately 20% of untested bulls will fail a bull BSE. All bulls should be tested each spring as fertility can chance with age, stress, and environment. By working with your veterinarian you can try to ensure a good calf crop the following spring.
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