Health and productivity of beef breeding bulls in Ontario

Abstract One hundred and seventy-eight randomly selected Ontario cow-calf herds were followed from breeding in 1986 to calving in 1987. The distributions of age, breed, culling, and disease for 315 breeding bulls and the patterns of bull management and usage in these herds are described. Potential associations between individual bull factors and bull fertility were examined for a subset of 134 bulls, from 106 herds, used in single-sire breeding groups. Limousin was the predominant bull breed. Hereford, Charolais and Simmental were also common. Lameness, both acute (6%) and chronic (5.7%), was the most frequently occuring disease class. Other diseases were recorded infrequently. The average sire age was 3 years. The overall culling rate was 26.1% and age-specific culling rates increased with age. Prebreeding soundness examinations were used rarely. Of the 315 bulls followed, 134 had been enroled in official growth-performance tests. The mean pregnancy rate in the 134 single-sire breeding groups was 92.7% and the mean group calving interval was 364.7 days (SD = 13.2). Chronic disease and supplemental grain feeding of bulls at selected periods in the year were associated with lower pregnancy rate. Both acute and chronic diseases of bulls were associated with increased mean group calving interval. Our analysis suggests that reproductive performance could be improved by better observation and replacement of diseased bulls just prior to and during the breeding season.