A bull may fail the first test, but can pass the second.
By: Robin Salverson, SDSU Extension, Cow/Calf Field Specialist
Breeding season is a few months away. However, it is time to start thinking about Breeding Soundness Exams (BSE) for your bulls. Herd bulls influence overall herd fertility more than any other single animal. Therefore a proper BSE for all herd bulls should be a very high priority.
What does a BSE include?
- Physical exam to determine the mating ability of the bull including feet and leg structure, eyes, teeth, penis, prepuce and body condition score of the bull.
- Scrotal circumference measurement. Why does the veterinarian measure the size of the scrotum? It is an indirect measurement of testicular tissue mass which is directly related to sperm quantity and quality. Likewise, bulls with smaller scrotal circumferences at one year of age had a small scrotal measurement at 2 years old. Additionally, abnormalities to the scrotum could be detected at this time.
- Semen Evaluation including motility and morphology. To pass a test, a bull must have at least a 30% sperm motility (headfirst movement) and 70% normal sperm morphology. Morphology refers to the number of normal sperm cells (without head, mid piece and tail defects). Studies indicate that bulls with 80% or better normal sperm can increase overall pregnancy rate.
Is a single BSE good for life?
- The answer is no. Several factors influence sperm production including injury, disease, fever, and extreme environmental condition. Also, injury to the penis and testes can affect fertility. In addition, young bulls’ semen quality can improve for up to 16 weeks following puberty.
When should be BSEs be conducted?
- Evaluation should occur 3 to 4 weeks prior to the breeding season. This allows for time to re-test the bull or find a replacement. A bull may fail the first test, but can pass the second. When relatively young bulls (around yearling age) are tested, this is not an uncommon occurrence.
Other factors to consider?
- Other factors to consider that are not measured by BSE are libido (desire to mate), servicing capacity and social dominance. All of these factors can affect a bull’s ability to breed, and therefore the success of the breeding season. Watch your bulls for these factors. General rule of thumb – if you are using a multi-sire pasture more bulls will be needed because several bulls will breed the same cow. Don’t put young bulls in breeding pastures with older bulls to avoid social dominance.
Contact your veterinarian to schedule your breeding soundness exam.