Saponins are glycosides found in many plants that have a
direct effect on rumen microbes. Saponins decrease protein
degradation and favour at the same time microbial protein
and biomass synthesis (Makkar and Becker, 1996), two
processes that result in reduced availability of hydrogen for
CH4 production (Dijkstra et al., 2007). However, the mode
of action of saponins seems to be mostly related to their
anti-protozoal effect (reviewed by Newbold and Rode,
2006). Recently, Guo et al. (2008) studied in vitro the effect
and mode of action of tea saponin on the rumen microbial
community and CH4 production. Tea saponin decreased
methanogenesis (28%) as well as the protozoal abundance
(2 50%). The activity of methanogens, as measured by the
mcrA gene expression, also decreased (276%) with tea