THE EFFECT OF CELL-WALL DEGRADING ENZYMES OR FORMIC-ACID ON FERMENTATION QUALITY AND ON DIGESTION OF GRASS-SILAGE BY CATTLE

A first cut of timothy, treated with water (untreated), formic acid (FA), cellulase + lactic acid bacteria (CB), cellulase + hemicellulase (CH) or cellulase + hemicellulase + a ligninmodifying enzyme (CHL), was ensiled in pilot-scale silos. Silages, except CB, were fed to four male cattle, each equipped with a rumen and duodenal cannula, in a digestibility trial designed as a 4 x 4 Latin square. The animals were fed a diet of 400 g of concentrate and 600 g of silage at a level of 70 g DM kg-1 live weight (LW0.75). All enzyme-treated silages were well-preserved with a more extensive fermentation than in FA silage. The quality of untreated silage was poorer as indicated by higher pH and ammonia-N content. The amount of effluent from enzyme-treated silages ranged from 116 to 127 g kg-1; for FA and untreated silages values were 101 g kg-1 and 80 g kg-1, respectively. Total DM losses from enzyme-treated silages were higher than from FA silage (P < 0.05). No significant differences were noticed between silages in the apparent digestibility of organic matter (OM), neutral-detergent fibre (NDF), acid-detergent fibre (ADF) or nitrogen (N). The apparent digestibility of cellulose was higher with enzyme-treated silages than with FA silage (P < 0.05). The values for microbial N flow at the duodenum were 80.0, 91.9, 80.7 and 70.5 g N d-1, and for the efficiency of rumen microbial N synthesis 38.6, 47.6, 36.9 and 32.5 g N kg-1 OM apparently digested in the rumen for untreated, FA, CH and CHL silages, respectively. In the rumen the molar proportion of propionate was higher (P < 0.01) and that of butyrate lower (P < 0.01) with enzyme-treated silages when compared with FA silage. The proportion of butyrate was also lower with untreated than with other silages (P < 0.01). The rumen residence time of NDF and ADF was longer (P < 0.05) with enzyme-treated silages than with FA silage.