Breeding soundness examination of North American bison bulls

Breeding soundness examinations were performed on two hundred and thirty-four 28- to 30-month-old bison bulls at Custer State Park from 1993 through 1997. Scrotal circumference (SC) was significantly associated with body weight, percentage of normal spermatozoa, percentage of primary spermatozoal defects, and percentage of motile spermatozoa. Larger SC was associated with increased odds of semen collection, satifsactory motility (greater than or equal to 30% motile spermatozoa), satisfactory morphology (greater than or equal to 70% normal spermatozoa), and simultaneous satisfactory motility and morphology. The optimal SC most predictive of simultaneous satisfactory spermatozoal motility and morphology was 29 cm. Only 36.2% of the bison bulls had a SC greater than or equal to 29 cm and satisfactory motility and morphology. We recommend use of 30% motility, 70% normal spermatozoal morphology, and 29 cm SC as minimal satisfactory measurements for BSE of 28- to 30-month old bison bulls that have been raised on a forage-based diet.