THE EFFECT OF LEVEL OF CONCENTRATE IN FEEDLOT DIETS ON GROWTH, HEALTH AND CARCASS CHARACTERISTICS OF BULLS

Two hundred and fifty-nine weaned bull calves (5.5 months old) from two calving seasons (1989 born = year 1, and 1990 born = Year 2) were used to study the effect of level of concentrate on their growth, health anal carcass characteristics. Eighty-six bulls were fed ad libitum concentrate (High), 88 restricted amounts of concentrate and ad libitum hay (Low) and 85 ad libitum concentrate and hay (Choice). Average daily gain (ADG) of bulls, on. High and Choice diets (1.8 kg d(-1)) was higher (P<0.05) than that on Low diet (1.3 kg d(-1)). Year 2 bulls on Low diet exhibited compensatory growth (2.0 kg d(-1)) when switched to Choice diet approximately 73 days prior to slaughter, and required only 8 anal 17 additional days, relative to bulls on High and Choice diets, respectively, to reach a carcass weight of 328.1 kg. Bulls on Low diet had no incidence of bloat (4.7% and 7.1% for High and Choice diets, respectively) and no incidence of respiratory infections in Year 2 (12.8% and 15.4% in High and Choice diets, respectively). All Year 1 bulls were treated for respiratory infections. At a constant slaughter age, carcasses of bulls on Low diet had lower (P<0.05) dressing percentage and fat thickness but higher cutability than those of High and Choice diets. These differences were not significant at constant fat thickness. Feedlot bulls cart, therefore, be fed a restricted concentrate and ad libitum hay diet for most of the growing period then switched to ad libitum concentrate and hay until bulls reach slaughter condition.