THE DETERMINATION AND CORRELATION OF REPRODUCTIVE PARAMETERS OF PERFORMANCE-TESTED HEREFORD AND SIMMENTAL BULLS

Purebred Hereford and Simmental bulls (n=120), managed similarly to bu lls in the Ontario Bull Evaluation Program, were evaluated for reprodu ctive parameters. Four diets, equivalent except for the form of dietar y fiber, were fed in a growth performance trial. Diet had no direct ef fect (P>0.10) on any of the reproductive variables examined. Of the 11 7 bulls that had complete breeding soundness evaluations, 75% were cla ssified as satisfactory potential breeders, 24% as questionable potent ial breeders and 1% as unsatisfactory potential breeders. The 2 breeds were significantly different (P<0.05) for several end of test paramet ers. When controlling for age and weight differences, Herefords had a higher backfat thickness, smaller scrotal circumference, lower paired testicular weight and lower epididymal weight. Semen morphology and mo tility did not differ (P>0.10) between the breeds. When examining simp le correlations, scrotal circumference was highly correlated with pair ed testicular weight, moderately correlated with epididymal weight, da ily sperm production and extragonadal sperm reserves, and negatively c orrelated with backfat thickness. Scrotal circumference was not relate d to backfat thickness when controlling for breed effects. The degree of germinal epithelium loss was moderately and negatively correlated w ith the percentage of spermatozoa with normal morphology and progressi ve motility, epididymal sperm reserves and epididymal weight, but was not correlated with scrotal circumference.