Although the spring calving season may still be ongoing in some operations, the next breeding season is only a few weeks away, meaning now is the time to schedule both old and new bulls for their pre-breeding soundness examination.
Bulls should be evaluated 30 to 60 days before the start of breeding, reminds Glenn Selk, Oklahoma State University Cooperative Extension emeritus animal scientist and editor of the OSU Cow-Calf Corner newsletter.
“It’s important to allow sufficient time to replace questionable bulls,” he said. “Bulls also could be evaluated at the end of breeding to determine if their fertility decreased.”
A breeding soundness exam is administered by a veterinarian and includes a physical examination of the feet, legs, eyes, teeth, flesh cover, scrotal size and shape; an internal and external examination of the reproductive tract; and semen evaluation for sperm cell motility and normality.
The physical examination studies overall appearance. Body condition can be affected by length of the breeding season, grazing and supplemental feeding conditions, the number of cows the bull is expected to service and the distance required to travel during breeding.
“Ideally, bulls should have enough fat cover at the start of breeding so their ribs appear smooth across their sides,” Selk said. “A body condition score 6 – where 1 is emaciated and 9 is obese – is the target body condition prior to the breeding season.”
Sound feet and legs are important because if they are unsound, this can result in the inability to travel and mount for mating. The general health of the bull is critical since sick, aged and injured bulls are less likely to mate and usually have lower semen quality.
The external examination of the reproductive tract includes evaluation of the testes, spermatic cords and epididymis. Scrotal circumference is an important measure since it is directly related to the total mass of sperm producing tissue, sperm cell normality and the onset of puberty in the bull.
“Bulls with large circumference typically will produce more sperm with higher normality and also reach sexual maturity sooner,” Selk said.
Examination of the external underline before and during semen collection will detect any inflammation, foreskin adhesions, warts, abscesses and penile deviations. The internal examination is conducted to detect any abnormalities in the internal reproductive organs.
“Cattle producers should make it a point to ask their veterinarian about the need to test the bulls for the reproductive disease trichomoniasis,” said Wes Lee, McClain County Extension director and agricultural educator.
The semen evaluation is done by examining a sample of the semen under a microscope. The veterinarian will estimate the percentage of sperm cells that are moving in a forward direction. This estimate is called "motility." In addition, the sperm cells will be individually examined for proper shape or "morphology."
“Fewer than 30 percent of the cells should be found to have an abnormal shape,” Selk said.
Any bull meeting all minimum standards for the physical exam, scrotal size and semen quality will be classed as a "satisfactory" potential breeder. Many bulls that fail any minimum standard will be given a rating of "classification deferred." This latter rating indicates the bull will need another test to confirm their status.
“Mature bulls categorized as ‘classification deferred’ should be retested after four to six weeks,” Lee said. “Mature bulls will be classified as ‘unsatisfactory potential breeders’ if they fail subsequent tests.”
It is not uncommon for young bulls just reaching puberty to be rated as "classification deferred" and then later meet all of the minimum standards. Therefore caution should be exercised when making culling decisions based on just one breeding soundness exam.
“The bottom line is cow-calf operators not only need to manage their cows for high fertility, they need to do likewise with their bulls and never just assume the animals will perform as expected,” Lee said.