The use of coarse maize silage as a dietary source of roughage for finishing Limousin bulls: effects on growth performance, feeding behaviour and meat quality

Two isonitrogenous, isocaloric and isofibrous diets for finishing beef cattle differing only in their roughage constituents were compared in a feeding trial with Limousin bulls. A control maize silage (chop length = 9 mm) and wheat straw were the roughage sources of the former diet representing 0.23 and 0.09 of the dietary dry matter (DM) respectively. These roughage sources were fully replaced in the latter by the inclusion of a coarsely chopped maize silage (19 mm) at a level of 0.45 of the total dietary DM. Two balanced groups of 20 Limousin bulls (425.8 +/- 20.3 kg live weight) each allotted in four pens were given the two diets ad libitum for a finishing period of 138 days. The different dietary roughages did not affect either bull growth performance (average daily gain = 1.39 +/- 0.25 kg/day) or food conversion ratio. However, the diet containing the coarse silage significantly (P < 0.05) reduced the intake of both DM (8.30 v. 9.02 kg/day) and neutral-detergent fibre (NDF) (2.64 v. 2.92 kg/day). Although total ruminating time was similar for both diets, bulls given the coarse maize silage diet spent more time ruminating 1 kg of DM or NDF, probably due to the higher percentage of dietary forage NDF. No food selection activity towards specific chemical constituents was observed in either diet. Slaughter measurements and meat quality were satisfactory and unaffected by the type of dietary roughage. Based on cattle growth performance, feeding behaviour, and meat quality, the use of coarse maize silage as a dietary source of roughage can be considered a feasible alternative in beef cattle finishing.