The effect of a silage additive and level of concentrate supplementation on silage intake, animal performance and carcass characteristics of finishing beef cattle

An experiment was carried out to examine silage fermentation, effluent production and aerobic stability in unwilted grass silage, which was either ensiled without additive or with a commercially available blend of ammonium hexamethanoate, ammonium hexapropionate and octanoic acid (6 l t(-1), Maxgrass, BP Chemicals Ltd., Northwich, UK) and to determine alternative approaches to obtaining the same performance in finishing beef cattle. Seventy-two Limousin x Friesian and Charolais x Friesian steers (mean initial live weight 424 kg s.d. 28.3) were blocked into groups of nine according to live weight and previous performance and offered silage, either with or without the additive, and supplemented with 0, 1.5, 3.0 or 4.5 kg d(-1) of a concentrate with a crude protein content of 150 g kg(-1) DM or allocated to a pre-experimental slaughter group to enable calculation of daily carcass gain. Daily silage intakes were recorded for 112 days. At the end of the experiment, all cattle were slaughtered and daily carcass gain, omental, mesenteric, perinephric and retroperitoneal fat depots [kidney-knob and channel fat (KKCF)], fatness, conformation, subcutaneous fat depth over M. longissimus dorsi muscle and carcass fat, protein and bone contents were assessed. Across all levels of supplementation, cattle offered the silage with the additive showed significantly (P < 0.001) higher daily DM intakes than those offered the silage without additive. Cattle offered the silage with the additive but unsupplemented had significantly (P < 0.001) higher daily carcass gains than those offered the silage without additive and unsupplemented. The response in carcass gain was 76 and 35 g kg(-1) additional concentrate for the silages with and without the additive respectively.