Effects of different molecular weights of chitosan on methane production and bacterial community structure in vitro

Abstract As a new feed additive, chitosan has been shown in recent years to have a certain role in reducing methane emissions from the gastrointestinal tracts of ruminants. However, the effects of chitosan with different molecular weights on rumen fermentation, methane production and bacterial community structure are not yet clear. A basal diet without chitosan served as the control (CTL), and the treatment diets were supplemented with chitosan with different molecular weights: 1 000 (1K), 3 000 (3K), 5 000 (5K), 50 000 (5W) and 200 000 (20W) dry matter (DM). Six fermentation units per treatment were established. Gas chromatography was used to measure the concentrations of methane, H2 and volatile fatty acids (VFAs). The bacterial 16S rRNA genes were sequenced with an Illumina MiSeq platform and analysed to reveal the relative abundances of bacterial community taxa. The results showed that the propionate proportion was significantly increased by the addition of chitosan with different molecular weights (P