AbstractA first cut of timothy, treated with water (untreated), formic acid (FA), cellulase + lactic acid bacteria (CB), cellulase + hemicellulase (CH) or cellulase + hemicellulase + a lignin‐modifying 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 × 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−1live 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−1and 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 70·5g N d−1, and for the efficiency of rumen microbial N synthesis 38·6, 47·6, 36·9 and 32·5 g N kg−1OM 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