In vitro assessment of the relationships between the digestion of different types of rice straw and bacterial community in the rumen

The aims of this study were to examine bacterial communities in relation to the rumen digestion of rice straw and to understand how concentrate supplements affect gut bacteria involving the digestion of a rice straw-based diet. The substrates were rice straw (RS) alone (experiment 1) and RS with 25% concentrates (barley and kidney beans) (experiment 2). The genomic DNA was collected to determine bacterial diversity by conducting denaturing gradient gel electrophoresis (DGGE). V6-V8 region group-specific (Clostridium and Bacteroides) primers were employed in the analyses. The DGGE band pattern was subjected to cluster analysis to demonstrate the similarity and difference between dietary treatments and solid-liquid fractions. Fibre digestibility, gas production, and volatile fatty acid (VFA) concentration were increased with incubation time. The differences between solid and liquid fractions were great in total bacteria, Clostridium, and Bacteroides communities. Clostridium and Bacteroides communities appeared unaffected by incubation time, whereas great differences existed between solid and liquid fractions throughout incubations (experiment 1). Barley and kidney bean supplements increased gas production and lowered rumen fluid pH, whereas changes in VFA concentration were significant only for kidney bean supplement. The Clostridium, and Bacteroides groups were affected by barley and kidney beans in the liquid fraction. However, the solid fraction was stable (experiment 2). These results indicate a rigid and stable community structure of Clostridium and Bacteroides groups involved in the digestion of rice straw-based diets in the rumen. Distinctive differences between solid and liquid fractions were described; hence, separate analyses of two fractions may greatly help understand the relationship between fermentation patterns and microbial communities in the rumen.