For example, if a bull has excellent scrotal circumference and excellent semen motility, but has a rear leg conformation that limits his ability to cover a breeding pasture, he fails the examination and is not considered a satisfactory breeder. A single failure does not mean a bull is subfertile. Semen samples collected from young bulls and bulls collected by electro-ejaculator can possibly consist of only accessory gland fluid and semen with poor motility. If these bulls are given a few days rest and tested again, a more representative sample could be collected. There are many causes of subfertility.
Heat stress is a common cause of subfertility.
In cases where a bull has had an elevated intratesticular temperature, abnormal sperm will appear in the ejaculate approximately two weeks after the heat stress and continue to increase for about one month. Normal semen is not ejaculated for about three months following the last day of heat stress. As opposed to heat stress, other abnormalities detected in a breeding soundness exam will not improve over time and the examiner will give a poor prognosis for recovery. Larson says by understanding the tremendous opportunity to improve your herd's fertility by rigorous use of the exam, and by grasping its limitations for individual bulls, producers can more effectively utilize this valuable tool. Larson warns producers that the results only reflect the bull's breeding soundness on the day tested.