In vitro gas production kinetics of grass silages treated with different cell wall-degrading enzymes

Grass was treated with six different cell wall-degrading enzymes and ensiled under different conditions dry matter (DM) content, stage of maturity]. Silage samples were dried, ground and incubated with buffered rumen fluid. Gas production was monitored over 48 h and gas production curves were fitted to a modified Gompertz equation.
In general, enzyme-treated silages showed a shorter initial lag phase and lower maximum gas production rate, indicating that the enzymes degraded cell wall material to more rapidly fermentable components, leaving a more slowly fermentable fraction. The total amount of gas produced was not altered by enzyme treatment, but a shift towards more rapidly fermentable material was observed. These changes in gas production kinetics went hand in hand with a change in chemical composition (more degradation of neutral detergent fibre and higher production of lactic acid in the enzyme-treated silages than in the control silages). Silages treated with enzyme preparations that did not contain cellulase did not differ from the control silages either in gas production kinetics or in chemical composition.
Wilting up to 300 g DM kg^?1 had no influence on gas production kinetics, whereas wilting up to 488 g DM kg^?1 resulted in a longer initial lag phase, a lower maximum rate and lower total gas production. With increased maturity, lower total amounts of gas and lower maximum rates were observed. The measurement of changes in gas production kinetics of enzyme-treated silages compared with control silages is a useful and rapid technique for prescreening the effects of enzyme addition.