ENZYMES AS SILAGE ADDITIVES .1. SILAGE QUALITY, DIGESTION, DIGESTIBILITY AND PERFORMANCE IN GROWING CATTLE

Four grass silages were made from perennial ryegrass ensiled after a 1h wilt in 2-t silos without additive application, with application of formic acid or with one of two enzyme mixtures of hemicellulases and cellulases (enzyme 1 and enzyme 2). Effluent losses were monitored over the ensiling period (130 d). Analyses of the silage showed that formic acid-treated silage had lower concentrations of lactic acid than the other silages. Both enzyme-treated silages had lower levels of cellulose, acid-detergent fibre (ADF) and neutral-detergent fibre (NDF) than the untreated and formic acid-treated silages. Effluent production was highest with enzyme-treated silages. The silages were subsequently fed to growing steers equipped with rumen cannulae and T-piece duodenal cannulae. Apparent whole-tract digestibilities of organic matter constituents were significantly lower (P < 0.05) with both enzyme-treated silages (untreated; 0.736, formic acid; 0.722, enzyme 1; 0.694, enzyme 2; 0.703). Both untreated and enzyme 2-treated silages sustained higher nitrogen digestibilities (g g-1 intake) (untreated; 0.675, formic acid; 0.636, enzyme 1; 0.630, enzyme 2; 0.662) and N retentions (g d-1) untreated; 16.0, formic acid; 14.0, enzyme 1; 11.6, enzyme 2; 16.6), but none of these differences was significant. When formic acid-treated silage was offered, there was a greater amount of organic matter apparently digested in the rumen (ADOMR). Non-ammonia nitrogen and microbial nitrogen flows at the duodenum were similar on all diets. The efficiency of microbial protein synthesis was highest with enzyme 2-treated silage and lowest with formic acid-treated silage (untreated, 35.4; formic acid, 25.2; enzyme 1, 30.4; enzyme 2, 39.4), but none of these differences were significant.