Supplementation of rice straw (Oryza sativa) with exogenous fibrolytic enzymes improves in vitro rumen fermentation characteristics


Abstract: A study was conducted to evaluate the use of exogenous enzymes as a potential means of improving the cell wall degradation of rice straw. The enzymes used for in vitro incubations were characterized for cellulase (CE) and xylanase (XY). Enzymes were supplemented alone (CE or XY) and as a mixture (CE + XY) in a 1:1 ratio. Five supplementation levels of enzymes including no enzyme (control) were used with 500 mg of ground (1 mm) substrate (rice straw) dry matter. Anaerobic buffer medium and strained ruminal fluid were added to the in vitro incubations in triplicate, and in vitro gas production (IVGP), in vitro rumen dry matter disappearance (IVRDMD), ruminal ammonia nitrogen (NH3-N), and volatile fatty acid (VFA) were determined. All enzyme treatments significantly increased (P < 0.05) IVGP and IVRDMD regardless of enzyme. The total NH3-N in fermentation liquid significantly increased under XY and CE4 (30.65 units of cellulase), and no differences were observed for CE + XY. No significant differences were observed for molar proportions of individual VFA, acetate:propionate ratio, or nonglucogenic ratio. The results reveal that use of fibrolytic enzymes is an effective way to improve the ruminal fermentation characteristics of rice straw.

Keywords: Ammonia nitrogen, cellulase, in vitro gas production, rumen dry matter disappearance, volatile fatty acid

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