Abstract An in vitro gas production (GP) technique was used to examine the effects of addition of an enzyme mixture (Natuzyme) on the GP profile of alfalfa hay, maize silage and wheat straw. The levels of enzyme inclusion were control (no enzyme), low (3 g of enzyme per kg dry matter (DM) of forage), medium (6 g enzyme per kg DM of forage) and high (9 g enzyme per kg DM of forage). Samples (200 mg) of each forage were incubated at 39 ◦C in triplicate in calibrated syringes containing buffered rumen fluid and GP (ml) was measured after 2, 4, 6, 12, 24, 48, 72 and 96 h of incubation. Addition of the enzyme had minor effects on in vitro gas production and fermentation kinetics of alfalfa hay and maize silage. However, there was a significant effect of the enzyme additive when used on the more fibrous roughage (wheat straw). The addition of enzyme increased cumulative gas production at 6 and 12 h of incubation when wheat straw was incubated, resulting in shorter lag times and changes in the shape of the gas production curves. Fractional fermentation rate of straw was increased with the low level of enzyme addition compared with the control, whereas this rate parameter was decreased when the enzyme was applied at the highest level of addition. These results suggest that addition of enzyme affects ruminal fermentation of forages differently depending on their fibre content and structural polysaccharide composition. The level of enzyme added is another important factor determining its efficacy, so that adding more than 3 g enzyme per kg DM of forage might not be beneficial. © 2008 Elsevier B.V. All rights reserved.

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