Effect of roughage source, protein and energy levels on in vitro fermentation and methanogenesis

Different substrate combinations (18) containing three roughages (wheat straw, paddy straw and sugarcane bagasse), three crude protein levels (7.2, 9.6 and 12% on DM basis) and two levels of TDN (48% and 60%) were tested for in vitro methane production and rumen fermentation metabolites. Total gas and methane production per gram of DM was higher (P<0.05) on high TDN ration and paddy straw as the roughage source, but the level of crude protein in diet did not affect these parameters. Methane production per gram of digested DM was higher (P<0.05) in low TDN (48%) ration and it was lower (P<0.05) when wheat straw was used as substrate as compared to the other two roughages. Crude protein and TDN contents in ration had no influence on carboxymethyl cellulase and xylanase activities, but these enzymes were lower (P<0.05) on sugarcane bagasse as compared to that on wheat straw or paddy straw. In vitro dry matter and organic matter degradabilities were higher on high TDN substrates, but CP content did not have any influence on these parameters. The degradability of feed was higher on paddy straw based substrates followed by those containing wheat straw and sugarcane bagasse. Acetate per cent in total VFA decreased and that of propionate increased on high TDN diets. Total as well as large and small oligotrichprotozoa were higher (P<0.03) on high TDN diet whereas holotrich populations were not affected. No effect of CP on protozoa population was observed. The results of the present study indicated that energy level had more pronounced effect on methanogenesis and ciliate protozoa than protein levels in diet and dietary manipulation appears to have a potential to reduce methanogenesis in the rumen significantly.