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

Purebred Hereford and Simmental bulls (n=120), managed similarly to bulls in the Ontario Bull Evaluation Program, were evaluated for reproductive parameters. Four diets, equivalent except for the form of dietary fiber, were fed in a growth performance trial. Diet had no direct effect (P>0.10) on any of the reproductive variables examined. Of the 117 bulls that had complete breeding soundness evaluations, 75% were classified as satisfactory potential breeders, 24% as questionable potential breeders and 1% as unsatisfactory potential breeders. The 2 breeds were significantly different (P<0.05) for several end of test parameters. 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 motility did not differ (P>0.10) between the breeds. When examining simple correlations, scrotal circumference was highly correlated with paired testicular weight, moderately correlated with epididymal weight, daily sperm production and extragonadal sperm reserves, and negatively correlated with backfat thickness. Scrotal circumference was not related to backfat thickness when controlling for breed effects. The degree of germinal epithelium loss was moderately and negatively correlated with the percentage of spermatozoa with normal morphology and progressive motility, epididymal sperm reserves and epididymal weight, but was not correlated with scrotal circumference.