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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.
Goel et al. (Wed,) studied this question.