Discussion 4.1. In vitro gas production, in vitro rumen dry matter disappearance, and ammonia nitrogen In agreement with the present results, Yang et al. (5) reported increased IVGP for rice straw supplemented with fibrolytic enzymes, while the same results were observed by Jalivaland et al. (6) when fibrolytic enzymes were added to wheat straw. In results similar to the present findings, Liu and Orskov (12) observed elevated IVGP in steam-treated rice straw supplemented with nonstarch polysaccharide enzyme. Although it is assumed that enzyme activity is suppressed after the initial phase of incubation, IVGP was higher with enzyme supplementation than in the control, which may be due to increased adsorption of enzymes to the feed during preincubation; this could increase the resistance of the enzymes to proteolysis and prolong their viability in the rumen.