Changes in microbial community structure, methanogenesis and rumen fermentation in response to saponin-rich fractions from different plant materials

Aims: Investigation of the effects of saponin-rich fractions on rumen fermentation, methane production and the microbial community. Methods and Results: Saponins were extracted from Carduus, Sesbania and Knautia leaves and fenugreek seeds. Two levels of saponin-rich fractions with a substrate were incubated using the Hohenheim gas method. Methane was measured using an infrared-based methane analyser and microbial communities using quantitative PCR. On addition of saponin-rich fractions, methane and short-chain fatty acid production was not affected. The protozoal counts decreased by 10-39%. Sesbania saponins decreased methanogen population by 78%. Decrease in ruminal fungal population (20-60%) and increase in Fibrobacter succinogenes (21-45%) and Ruminococcus flavefaciens (23-40%) were observed. Conclusions: The saponins evaluated possessed anti-protozoal activity; however, this activity did not lead to methane reduction. Fenugreek saponins seemed to have potential for increasing rumen efficiency. The saponins altered the microbial community towards proliferation of fibre-degrading bacteria and inhibition of fungal population. Significance and Impact of the Study: The uni-directional relationship between protozoal numbers and methanogenesis, as affected by saponins, is not obligatory. All saponins might not hold promise for decreasing methane production from ruminants.