PROTEIN SUPPLEMENTATION OF FORMIC ACID-TREATED AND ENZYME-TREATED SILAGES .1. DIGESTIBILITIES, ORGANIC-MATTER AND FIBER DIGESTION

Two silages were made from perennial ryegrass ensiled without wilting in 2-t capacity silos with the application of either formic acid or an enzyme mixture of cellulases and hemicellulases. Effluent losses were monitored over the ensiling period. Subsequent silage analysis showed that the enzyme-treated silage had higher concentrations of residual water soluble carbohydrate, lactic acid and acetic acid, and lower concentrations of cellulose, ADF and NDF. Effluent production was higher with the enzyme silage (formic acid, 211 l t-1; enzyme, 267 l t-1). The silages were either offered as the sole diet or supplemented with rapeseed meal at two levels (60 or 120 g fresh weight kg-1 silage DM offered) to growing steers equipped with rumen cannulae and T-piece duodenal cannulae. Apparent whole tract digestibilities for DM, OM, N, ADF and NDF were similar for all diets although nitrogen retention (g d-1) was increased with supplementation of both silages (formic acid, 21.1; formic acid + 60 g, 23.5; formic acid + 120 g, 28.5; enzyme, 22.6; enzyme + 60 g, 25.8; enzyme + 120 g, 31.6). Rumen pH, ammonia and total volatile fatty acids patterns were similar. Supplementation increased the amount of organic matter apparently digested in the rumen (ADOMR) with formic acid-treated silage but not with enzyme-treated silage. Liveweight gains were similar for both unsupplemented silages (0.49 kg d-1). These increased to 0.55 and 0.65 kg d-1 for formic + 60 and formic + 120 respectively. Liveweight gains for the corresponding enzyme-treated supplemented diets were 0.81 and 0.91 kg d-1 respectively. Liveweight gains on supplemented enzyme-treated diets were significantly (P < 0.05) greater than those on formic acid-treated diets.