AbstractThe effects of two commercial cellulase/hemicellulase enzymes derived fromTrichoderma reeseion silage fermentation were investigated in three laboratory‐scale experiments. In Experiment 1, perennial ryegrass (Lolium perenne) was treated with enzyme A at the rates of 0, 0·125, 0·250, 0·500 and 0·750 cm3kg‐1. In Experiment 2, Italian ryegrass (Lolium multiflorum) was treated with the same enzyme at the rates of 0, 0·250 and 0·500 cm3kg‐1and with 85% formic acid (3·5 cm3kg‐1). In Experiment 3, perennial ryegrass was ensiled untreated, with enzyme A (0·250 and 0·500 cm3kg‐1) and with 0·200 and 0·400 cm3kg‐1enzyme B which also contained glucose oxidase. All silages were well preserved. In general enzyme treatment reduced pH and the contents of ammonia nitrogen, neutral detergent fibre and acid detergent fibre, whereas the contents of water‐soluble carbohydrates, acetic acid, lactic acid an