Predicting natural-mating efficiency in beef bulls from a sample of semen

NIneteen Angus and 14 Polled Hereford bulls were used to determine the relationship of certain semen characteristics with subsequent fertility. Semen samples were obtained from bulls by electroejaculation. Measurements obtained from each sample were volume, concentration (billions per milliliter), percent motility, vigor (degree of motility), and percent abnormal spermatozoa. Cows of various ages and parities were used in single-sire breeding groups for evaluation. Weighted-means adjusted for parity were obtained to evenly weigh the cow herd. These overage values were used to more effectively evaluate the individual bull's potential fertility. The results of this study show that percent abnormal spermatozoa and percent motility best predicted how the bull would perform in the field. Percent abnormal sperm and motility could cause lower conception when slight fluctuations in their measurements were evident. Use of these criteria and this type of evaluation represents one of the most economical and fastest approaches to determine the beef bull's potential fertility.