Repro Tracks
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ANGUSJournal n September 2011 Breeder question No. 1 Which is more important when doing a bull BSE, measuring a bull’s scrotal circumference or evaluating the semen that he produces? Response: Scrotal measurements and semen characteristics are both important! This is proven by the change made in the Society for Theriogenology’s breeding soundness exam in 1992. The exam was changed from a numerical scoring system to a system employing minimum threshold standards for scrotal circumference, sperm motility and sperm morphology. Prior to 1992 measurements of scrotal circumference, sperm motility and sperm morphology were each given a numerical score. The scores were added up to determine if a bull passed the exam. In some cases a bull could be marginal or deficient in one area — for example, have a very small scrotal circumference — but produce semen with excellent motility and quality and thereby have a total score that enabled him to pass the exam. When it became apparent bulls that passed the breeding soundness exam but were deficient in one part of the exam were more likely to have breeding problems, the scoring system was changed. Now a bull must exceed the minimum acceptable level for each of the three traits related to semen production. Therefore, the Society for Theriogenology views both scrotal circumference and semen characteristics to be critical in predicting the breeding soundness of a bull. Scrotal circumference is measured because it is highly correlated (0.92) with testis weight. Hence, scrotal circumference is the best estimate of a bull’s maximum daily sperm production. In contrast, sperm motility and morphology are used to estimate the proportion of the sperm produced by a bull that are alive and have a normal shape. Percent live and percent normal sperm are related to the chance of fertilization and successful embryo development occurring after a cow is bred by the bull.
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