Exogenous enzymes added to untreated or ammoniated rice straw: Effects on in vitro fermentation characteristics and degradability

A study was conducted to evaluate the use of exogenous enzymes as a potential means of improving the cell wall degradation of rice straw. Two developmental cellulases (END), two developmental xylanases (XY), and two commercial enzyme products (EX, supplying a combination of endoglucanases and xylanases; PROT, supplying mostly proteases) were evaluated for their potential to improve in vitro degradation of untreated (URS) or ammoniated rice straw (ARS). The END and XY were added to milled samples (0.45 g dry matter [DM]) of URS and ARS at a rate of 200–300 International Units (IU) of endoglucanase or xylanase. The EX supplied 200–300 IU each of endoglucanase and xylanase, whereas PROT supplied mostly protease. Anaerobic buffer medium and strained ruminal fluid were added to the in vitro incubations and gas production (GP) was measured during 24 h of incubation. Degradabilities of DM, neutral detergent fibre and acid detergent fibre, and volatile fatty acid profiles were determined at the end of the 24 h incubation. Overall, GP and degradability of rice straw were greatly increased by ammoniation. Adding EX or PROT enzymes increased (P