The mechanism of antimethanogenic bioactivity of plants in the rumen

Summary

We have examined several aspects of plant bioactivity against methane production by rumen microbes.  We have isolated and examined the effect of plant fractions and purified compounds in mixed rumen populations (batch culture or RUSITEC), as well as in pure culture of rumen methanogens.  In these systems, we measured the effect on rumen activity, microbial end-products, shifts in microbial populations, persistency and possible adaptation to the bioactive additive, as well as the mechanism of the effect.

While we have isolated several potent antimethanogenic fractions amongst additional plants that were likely to be tannins, we have found that extractable non-tannin compounds are responsible for the antimethanogenic effect in the bioactive plants Eremophila glabra and Biserrula pelecinus.  Using a bioassay-guided fractionation, we have isolated multiple potent antimethanogenic fractions from these.  Fractions from B. pelecinusalso had a potent effect against key methanogens, with one fraction producing aneffect that was close to cidal. 

Finally, we have found antimethanogenic properties amongst several commercial plant bioactive products,including grape marc, L, C and G.  In the later, we confirmed that the antimethanogenic effect may persist over two weeks without disrupting normal rumen fermentation. These compounds had a very potent effect in pure culture of methanogens and further workon these isneeded.