Effects of mixed modes on fermentation quality and In vitro gas dynamics of sorghum-sudangrass hybrid (Sorghum bicolor x S. sudanense) silage

Sorghum-sudangrass hybrid silage has poor fermentation characteristics owing to a high moisture content. Accordingly, a 3 x 4+1 factorial design was applied to investigate the effects of adding different types and amounts of hay (corn stalk. wheat straw, and alfalfa hay at 12.5 kg t(-1), 25 kg t(-1), 37.5 kg t(-1), and 50 kg t(-1)) on the nutritive value, fermentation quality, 72 h dry matter digestibility, and gas dynamics in vitro to simulate the rumen fermentation of sorghum-sudangrass hybrid silage. Separated silage of sorghum-sudangrass hybrids had a high butyric acid content and a FLIEG's scores evaluation ranking of only "Fair." The addition of hay significantly improved the fermentation quality of mixed silage. With respect to hay type, adding wheat straw had the best fermentation quality, alfalfa hay had the best nutritive value, in vitro dry matter digestibility (IVDMD) (662.41 g kg(-1)), constant fractional rate (C) (0.28 mL h(-1)), and the average gas production rate (AGPR) (32.48 mL h(-1)) content. There were no differences in the cumulative gas production at 72h (GP(72h)), asymptotic gas production generated at a constant fractional rate (A), and lag time before gas production commenced (lag) among the three hay types. With respect to quantity, 25 kg t(-1) hay had the best fermentation quality, 50 kg t(-1) hay had the best nutritive value and highest IVDMD content (662.81 g kg(-1)). 37.5 kg t(-1)hay had the highest C (0.28 mL h(-1)) and AGPR (31.48 mL h(-1)) contents, 25 kg t(-1) hay had the highest Half time (2.20 h), and there were no significant differences in GP(72h), A, and lag among the four amounts. Considering both nutritive value and fermentation quality, the best mixed silage mode was 37.5 kgt(-1) wheat straw.