Effects of supplementary concentrate level with grass silage, and separate or total mixed ration feeding, on performance and carcass traits of finishing steers

Abstract

Concentrates are a major component of feed costs in winter finishing of beef cattle. The objectives of this study were (1) to determine the response to increasing levels of supplementary concentrates with grass silage, and (2) to determine the effects of feeding silage and concentrates separately or as a total mixed ration (TMR). A total of 117 finishing steers (mean initial live weight 538 (s.d. 35.5) kg) were assigned to a pre-experimental slaughter group of 9 animals and to 6 feeding treatments of 18 animals each. The feeding treatments were (1) silage only offered ad libitum (SO), (2) SO plus a low level of concentrates offered separately (LS), (3) SO plus a low level of concentrates offered as a TMR (LM), (4) SO plus a medium level of concentrates offered separately (MS), (5) SO plus a medium level of concentrates offered as a TMR (MM), and (6) concentrates ad libitum plus a restricted silage allowance (AL). Low and medium concentrate target levels were 3 and 6 kg dry matter (DM) per head daily. When silage (210g/kg DM, 758 g/kg in vitro DM digestibility, pH 3.7) and concentrates were fed separately, the daily concentrate allowance was given in one morning feed. The animals were individually fed for a mean period of 132 days. After slaughter, carcasses were weighed and graded and a rib (6th to 10th) joint was dissected into its component tissues. Silage DM intake decreased (P < 0.001) but total DM intake increased (P < 0.001) with increasing concentrate level. Average live-weight gains for SO, LS, LM, MS, MM and AL was 0.34, 0.86, 0.86, 1.02, 1.00 and 1.12 (s.e. 0.064) kg/day, respectively. Corresponding carcass weight gains were 0.25, 0.58, 0.58, 0.71, 0.68 and 0.82 (s.e. 0.028)kg/day. All measures of fatness increased (P < 0.05), bone proportion of the rib joint decreased (P < 0.001), and muscle proportion was not significantly affected by dietary concentrate level. There were no significant interactions between concentrate level and method of feeding. Compared with offering the feeds separately, feeding as a TMR increased silage DM intake by proportionately 0.06 (P < 0.05) and total DM intake by proportionately 0.04 (P < 0.05). Method of feeding had no significant effect on performance, slaughter or carcass traits. It is concluded that silage intake decreased and total intake increased with increasing concentrate level. Live-weight and carcass-weight gains also increased with increasing concentrate level. Feeding a TMR had no effect on animal performance or carcass traits compared with separate feeding.