Global warming and climate change have become global issues. One of the main greenhouse gases (GHG) is CH4, which
increased by about 40% in the atmosphere from 1970 to 2004 (IPCC, 2007). Methane has a heat trapping potential 23 times
that of CO2 (IPCC, 2001). On a global scale, enteric CH4 produced by domesticated ruminants contributes 0.18 of total
GHG emissions (FAOSTAT, 2006). CH4 production by ruminants also results in a loss of gross energy intake of up to 0.12
(Johnson and Johnson, 1995). Therefore, reduced CH4 production by ruminants has been recognized as an important goal because it reduces the GHG emission and improves feed efficiency. Enteric CH4 is a product of anaerobic fermentation in the rumen which is produced by methanogenic archaea during disposal of metabolic H2 produced by their metabolic activity.
In the rumen ecosystem, rumen protozoa are also involved in methanogenesis because of their ecto- and endo-symbiotic
association with methanogenic archaea which utilize H2 produced by the protozoa to produce CH4 (Vogels et al., 1980).