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

Two hundred and fifty-nine weaned bull calves (5.5 months old) from tw o calving seasons (1989 born = year 1, and 1990 born = Year 2) were us ed to study the effect of level of concentrate on their growth, health anal carcass characteristics. Eighty-six bulls were fed ad libitum co ncentrate (High), 88 restricted amounts of concentrate and ad libitum hay (Low) and 85 ad libitum concentrate and hay (Choice). Average dail y gain (ADG) of bulls, on. High and Choice diets (1.8 kg d(-1)) was hi gher (P<0.05) than that on Low diet (1.3 kg d(-1)). Year 2 bulls on Lo w diet exhibited compensatory growth (2.0 kg d(-1)) when switched to C hoice 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 di et 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 (1 2.8% and 15.4% in High and Choice diets, respectively). All Year 1 bul ls were treated for respiratory infections. At a constant slaughter ag e, carcasses of bulls on Low diet had lower (P<0.05) dressing percenta ge and fat thickness but higher cutability than those of High and Choi ce diets. These differences were not significant at constant fat thick ness. Feedlot bulls cart, therefore, be fed a restricted concentrate a nd ad libitum hay diet for most of the growing period then switched to ad libitum concentrate and hay until bulls reach slaughter condition.