Breeding Soundness Evaluation of Bulls

Very few bulls are “sterile” and unable to produce any offspring. But, 10% to 25% of bulls have reduced fertility or possess physical problems which reduce their ability to sire calves. The breeding soundness evaluation (BSE) is a useful tool in identifying these bulls. Eliminating bulls with physical problems or reduced fertility from the breeding herd will improve overall reproductive efficiency of the herd. A standardized procedure has been developed and refined during many years of use, along with research to validate the accuracy. The current standards were adopted in 1992. When this procedure is carefully followed the results are consistent for assorted breeds, locations and veterinarians. However, if shortcuts are taken from the standard procedure, the results are erratic and inconsistent. For example, if a veterinarian evaluates the semen only for sperm motility, the abnormalities of sperm morphology (shape) will be missed and this will result in a different and misclassification of the bull’s fertility. It is critical that each step in the procedure be followed. It is also important to remember that the BSE is only a “snapshot” on that one day, and subsequent injury or illness may change the classification and fertility of the bull. A major problem in conducting BSEs on young bulls is the variability in their sexual maturity at the time of evaluation. Many bulls are initially evaluated by a BSE at 11 to 13 months of age, yet some bulls will not reach sexual maturity until 15 to16 months. Sexual maturity cannot be predicted entirely by body weight, or even by scrotal circumference. Some young bulls deemed not acceptable by the test at a young age may be satisfactory breeders if re-tested 1 to 3 months later. Approximately 75 days are required for the bull to produce semen. Sperm production requires about 60 days and an additional 15 days are required for transport through the system, during which further sperm maturation occurs. It is critical for the evaluating veterinarian to remain neutral between seller and buyer during the evaluation, even though it is often the seller who is paying for the BSE, prior to a sale. The evaluator cannot allow that source of payment to tilt the evaluation in favor of the seller, but must remain neutral and follow all the prescribed BSE procedures. Anything less is unfair to the buyer, who is expecting to purchase a bull that is ready to breed and who may put the bull in with females the day after purchase. Producers also need to recognize that a BSE does not evaluate a bull’s breeding drive or ability. Other tests could be conducted for this type of evaluation, but they are involved and time consuming. If these tests are not conducted the producer should ensure that bulls, especially new ones, are observed during the breeding process and that they are interested and able to mount and inseminate females. This is another critical test. A BSE consists of three steps or parts: 1. A physical exam including the internal and external reproductive structures. 2. A measurement of scrotal circumference; 30 cm is the minimum acceptable size for even young bulls, and the size requirement increases with age. 3. Collection and evaluation of semen. At least 30% motility and 70% normal morphology are required as a minimal acceptable level. The standardized procedure of evaluation will result in a classification into one of three categories: a. “Satisfactory” potential breeder b. “Unsatisfactory” potential breeder c. “Classification Deferred” (with a recommended date for re-evaluation)