Bull Breeding Soundness Exam

       Producers searching for a cost efficient method to promote a successful breeding program may find breeding soundness examinations (BSEs) for bulls beneficial. The importance of the bull in a cattle breeding program often is underestimated. A cow is responsible for half the genetic material in only one calf each year, while the bull is responsible for half the genetic material in 20 to 50 calves. The bull's ability to locate cows in estrus and breed them is clearly vital to a successful breeding program.

     For the breeding soundness evaluation to be successful, bulls should be evaluated 30 to 60 days before the start of breeding. It is important to allow sufficient time to replace questionable bulls. Bulls should also be evaluated at the end of breeding to determine if their fertility decreased. A BSE is administered by a veterinarian and includes a physical examination (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. Flesh cover is one factor to evaluate. Body condition can be affected by length of the breeding season, grazing and supplemental feeding conditions, number of cows the bull is expected to service and 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. A body condition score 6 (where 1 = emaciated and 9 = very obese) is the target body condition prior to the breeding season.

     Sound feet and legs are very 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 and his female offspring. Bulls with large circumference will produce more sperm with higher normality and also reach sexual maturity sooner.

     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.

     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". Less than 30 percent of the cells should be found to have an abnormal shape.

     The effect of semen quality on fertility is well documented in numerous research studies. The next two tables illustrate the impact of semen quality on fertility rates. Table 1 illustrates that bulls classified as satisfactory had a 60 percent first-service conception rate, while those that were classified as unsatisfactory had a 30 percent first-service conception rate. In further work, by Wiltbank (table 2) bulls that were classified as having semen with 80 percent or more normal sperm, the pregnancy rates in cows mated, averaged 91.5% compared to 86% for randomly selected bulls. That magnitude of difference may be small, but economically to a cow-calf operation it is very large. Another 6 calves for every one hundred cows exposed would more than pay the bill on the breeding soundness exams for 4 bulls.

Beef Cattle Bull Semen Quality

     Any bull meeting all minimum standards for the physical exam, scrotal size and semen quality will be classed as a "satisfactory" potential breeder. Bulls that fail any minimum standard will be given a rating of "classification deferred."

     This rating indicates that the bull will need another test to confirm status. Mature bulls should be retested after six weeks. Mature bulls will be classified as unsatisfactory potential breeders if they fail subsequent tests. Young bulls that are just reaching puberty may 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.

     Many producers work hard to manage their cows for high fertility. They may assume that the bulls will do their expected duties. However, it's important to pay close attention to bulls to establish successful breeding.

OSU Cow/Calf Corner

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 Red Beef Cattle Barn