By Dr. Megan Van Emon, Montana State Beef Cattle Extension Specialist
One of the most cost efficient methods of a successful breeding program is the breeding soundness exam (BSE) conducted on bulls. Bulls are responsible for breeding 20 to 50 cows each breeding season while cows are responsible for one calf each year. Having a BSE conducted on the bulls is crucial to a successful breeding program.
The BSE is an exam conducted by veterinarians that includes a physical exam, semen evaluation, and an internal and external exam of the reproductive tract. Evaluating the feet, legs, teeth, eyes, flesh cover, and scrotal circumference and shape is included in the physical exam. The semen evaluation includes semen normality and motility. The BSE should be conducted 30 to 60 days prior to the beginning of breeding. It is important to note that the bull’s sperm production cycle is approximately 60 days, and if illness, injury or other issue occurs, this could negatively impact the BSE and breeding capability of the bull and may need to be re-evaluated. An additional BSE can be conducted at the end of the breeding season to determine if bull fertility decreased throughout the breeding season.
Body condition is crucial for bulls during the breeding season. Having adequate flesh cover during the breeding season is needed to provide the extra energy required for breeding. Body condition can be impacted by the number of cows the bull is expected to breed, the distance traveled to breed or eat, and nutrition during the breeding season. A body condition score 6 or sufficient body condition that the ribs appear smooth across the bull’s side is the ideal flesh cover at the start of the breeding season.
Ensuring bulls are structurally sound in their feet and legs is needed to begin the breeding season. Bulls with unsound feet and legs will have a difficult time walking and mounting for mating if a significant distance needs to be traveled for breeding. General health of the bull is also needed to ensure bulls have adequate semen quality and the ability to mate. Scrotal circumference is an essential measure because it is directly related to sperm production, sperm normality, and the onset of puberty. The external and internal reproductive tract examinations ensure there is no inflammation, abscesses, warts, or penile deviations.
The semen evaluation includes the measurement of semen motility or the percentage of sperm cells moving in a forward direction. The bulls needs to at least have 30% sperm motility to pass the BSE. Sperm morphology, or the proper shape, is also determined and at least 70% of the sperm cells should have a normal shape.
If all of the minimum requirements are met, the bull will be classed as “satisfactory.” However, if a bull does not pass one of the tests, they will be classed as “classification deferred.” If a bull is classed as “classification deferred,” the bull should be tested again after 6 weeks. If a mature bull fails the subsequent BSEs, they will be classified as “unsatisfactory.” A young bull may be “classification deferred,” and pass the subsequent test. Exercise caution when making bull culling decisions based on a single BSE.