Bull Breeding Soundness Exam

Barry Whitworth, DVM Area Food/Animal Quality and Health Specialist for Eastern Oklahoma

The time to prevent a lice infestation in your cattle is now. Remember that many products require two applications to be effective. Photo by Amanda Lester.

As November approaches, the fall calving season should be coming to an end which means that it is time to get the bulls ready to turn out for breeding. All bulls should have a breeding soundness exam (BSE). A BSE is a procedure performed by a veterinarian that ensures a bull has met a minimal set of standards that reflect his reproductive potential. The exam is not a guarantee that the bull will breed cows because some bulls are not aggressive breeders. However, the test does ensure that the bull has the potential to breed cows. The exam does have limits. The exam is only true at the time of the test and cannot ensure results for the future. The exam has three components. A physical exam is performed to ensure that the bull is in good health. A reproductive exam evaluates the health of the reproductive organs. The final component is an evaluation of the semen for motility and normality. This small investment in a BSE to ensure a fertile bull may reduce the number of cows found open when they are pregnancy checked.

The BSE begins with a general physical exam. The breeding bull should have a body condition score of 6.  Since a good aggressive breeding bull will most likely lose weight, a bull in poor body condition may not service cows as the breeding season progresses for lack of stamina. A bull will be on the move during the breeding season, so good mobility is essential. Any feet, joint, or leg problems would be considered not satisfactory. A bull should have good eyes for finding those cows in heat. Any abnormality in the physical exam is a cause for concern.

Next, the veterinarian will evaluate the internal and external reproductive organs. A rectal exam is performed to assess the internal organs for any abnormality. Organs that are abnormal will likely affect semen quality. The scrotum is examined and measured. The testicles should be of similar size and move freely in the scrotum. The testicles should not be soft or have any palpable abnormalities. A scrotum that only has one testicle is a disqualification. The skin is examined for abnormalities such frost bite.  Problems in the skin could result in problems regulating the temperature of the testicles. Variations in temperature could result in abnormalities in the sperm. The size of the scrotum is measured in centimeters. A scrotal measurement of 30 cm is required for bulls of 15 months of age and the minimal size increases with age up to 2 years which is 34 cm. Scrotal size gives an estimate of the daily sperm production. During the collection process, the penis will be examined for any growths, hair rings, warts, or damaged which may affect the bull’s ability to breed.

The final part of the BSE is the evaluation of the semen. Once a sample is obtained, the veterinarian will place a drop of semen diluted with saline on a slide and examine it under the microscope for motility. A motility score will be based on individual progressive motility. Progressive motility means that the sperm are moving in one direction and not just spinning in a circle. The minimal acceptable score is 30% of the sperm have progressive motility. The veterinarian will next examine the morphology of semen. Morphology is looking for normal and abnormal sperm. A minimal score requires that 70% of the sperm must be normal. Producers should refrain from assuming that if a bull has a high motility and morphology score that this makes the bull a superior breeder. The breeding ability of the bull is not improved based on a higher score.

Once the exam is completed, the bull with be classified as a “satisfactory potential breeder”, “unsatisfactory potential breeder”, or “deferred”. The “satisfactory potential breeder” has met the minimal levels for scrotal circumference, sperm motility, and sperm morphology. As well as the bull’s physical and reproductive exams were acceptable. An “unsatisfactory potential breeder” has not met the minimal standards and/or has a physical or reproductive problem that is highly unlikely to improve over time. A “deferred” classification means that the bull did not meet the minimal standards and/or has a physical or reproductive problem that with time may improve. “Deferred” bulls should be retested at a later date. The “deferred” classification is not uncommon for immature bulls.

A BSE does not detect infectious diseases that might be present in the bull. These diseases may cause infertility or other reproductive problems. Testing for diseases such as Trichomoniasis or Persistently Infected Bovine Virus Diarrhea might prevent unwanted infections in the cow herd. This is a convenient time to obtain the samples necessary to complete these tests.

Studies have been done that compare untested bulls to those that have passed a BSE. Bulls turned in with cows that passed a BSE get more cows settled than untested bulls. Also, BSE tested bulls get cows settle earlier in the breeding season. Earlier pregnancy equals calves being born early in the calving season. Producers should consider the cost of a BSE as an insurance. For more information about BSE, please contact the local veterinarian or the local Oklahoma State University County Extension Agriculture Educator.

Read more in the November 2020 issue of Oklahoma Farm & Ranch magazine.