The internal sex organs should be palpated rectally to ensure proper development and size. Good vision and sound feet and legs should also be considered when evaluating a bull's physical abilities to breed. Scrotal circumference gives an indication of a bull's ability to produce sperm and is related to younger age at puberty. Breeds differ somewhat as to scrotal circumference, but 32 centimeters is generally accepted as the minimum size for yearling bulls to be sound breeds. Four criteria are used to evaluate semen, i.e., volume, concentration, motility and morphology.
Proper training is required to accurately evaluate semen.
A scoring system for predicting potential breeding soundness of bulls as prepared by the Society for Theriogenology, which incorporates scrotal circumference, semen motility, and semen morphology, is shown in Table 1. Breeding soundness examinations presently do not include an evaluation of a bull's sexual drive or libido. Libido testing is time consuming and requires use of females in estrus and therefore is difficult to conduct on a large scale. Procedures are being investigated to better evaluate the willingness and desire of bulls to mate. Copyright 1999 University of Missouri.