A small scale rumen incubation system to screen chemical libraries for potential methane inhibitors

There is currently an urgent need for effective anti-methanogen small molecule inhibitors to help control ruminant methane emissions on a global scale. No assays system has yet been reported that would enable high-throughput screening of either rumen methanogen cultures or an assay system that utilises rumen fluid. We report here the development of a high-throughput 0.2 ml rumen fluid-based 96-well screening system that incorporates a simple substrate for fermentation with a short incubation time The fermentation parameters determined are total gas, methane and hydrogen production. The system markedly enhances the number of samples that can be processed (∼1000 incubation vials per week) compared to previously published assays. The system does not try to mimic rumen fermentation but is a means of screening compounds for their potential effect against rumen methanogens. We also assessed the system using known rumen anti-methanogen inhibitory compounds, a set of anthraquinone derivatives and 3-nitrooxypropanol. The system can differentiate between specific methane inhibition and the inhibition of overall fermentation and it discriminates between molecules that act as methanogen inhibitors and those acting as electron sinks.