A comparison of silage-based and dried forage-based diets for finishing beef cattle

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Abstract
Two experiments have been carried out to compare silage-based and dried forage-based diets for finishing beef cattle, and to examine the effect of supplementing the silage-based diet with additional protein. The three diets used in experiment 1 consisted of (1) grass silage supplemented with a low-protein, cereal-based concentrate (98 g crude protein (CP) per kg dry matter (DM)) (2) grass silage supplemented with a high-protein, cereal/soya-bean meal concentrate (208 g CP per kg DM) and (3) grass hay supplemented with a cereal-based concentrate (130 g CP per kg DM). The two diets used in experiment 2 consisted of (1) grass silage supplemented with barley and (2) a mixture of grass hay and artificially dried grass supplemented with barley. All the diets contained approximately 700 g forage and 300 g concentrates per kg DM except diet 3 in experiment 1 which contained 240 g hay and 760 g concentrates per kg. The silages were of high digestibility (digestible organic matter in dry matter 0·72) and were well preserved (ammonia N 36 g/kg total N). The diets were offered to castrated male cattle which were initially 384 kg in experiment 1 and 515 kg in experiment 2. For diets 1 to 3 in experiment 1 and diets 1 and 2 in experiment 2 respectively metabolizable energy intakes were, 92, 94, 94, 124 and 120 MJ/day; live-weight gains were 1·21, 1·16 and 1·21 (s.e. 0·044) and 1·25 and 1·22 (s.e. 0·060) kg/day; carcass gains were 0·76, 0·76 and 0·75 (s.e. 0·034) and 0·80 and 0·74 (s.e. 0·036) kg/day; carcass fat classifications (five-point scale; 1 = leanest, 5 = fattest) were 2·4, 2·9 and 2·2 (s.e. 0·09) and 3·6 and 3·6 (s.e. 0·18); mean subcutaneous fat depths were 6·8, 8·1 and 6·6 (s.e. 0·74) and 7·8 and 7·4 (s.e. 0·48) mm; areas of m. longissimus dorsi at the 10th rib were 66·4, 69·4 and 71·3 (s.e. 3·16) and 77·6 and 72·3 (s.e. 1·52) cm2 and marbling scores (eight-point scale; 1 = leanest, 8 = fattest) for m. longissimus were 1·7, 2·5 and 2·2 (s.e. 0·24) and 3·2 and 2·8 (s.e. 0·16). It is concluded that performance, efficiency of energy utilization and carcass fatness were similar for silage-based and dried forage-based diets, and that protein supplementation of a silage-based diet did not affect performance but tended to increase carcass fatness.