Yak is lower methane producer than cattle, in spite of the fact that both the animals are fed similar diets and there are only small variations between the microbiomes of both the animals. Lower methane and hydrogen yields in yak vs cattle are 0.26 vs 0.33 mmol methane/g dry matter intake and 0.28 vs 0.86 mmol/d hydrogen generation have been reported. Hydrogen recovery from cattle was significantly higher than that from yak (Mi et al., 2017). There were a few higher abundant bacteria in the yak species, which would produce less hydrogen, in comparison to that in cattle. However, in the abundance of methanogens, there was no difference between the two animal species. It is therefore, hypothesized that…show more content… Therefore, these compounds have been used as medicine in traditional system of medicare in India, Pakistan, China, Srilanka, Japan and other Asian and African countries These are also used for preservation of foods and as spices in kitchen in many parts of the world since time immemorial. More than 200,000 defined structures of plant secondary compounds have been identified. These PSM can generally be classified into three major groups: saponins, tannins and essential oils (EO) (Kamra et al., 2008).
Plant secondary metabolites might inhibit methane emission by the following modes:
• They might directly inhibit methanogens as these compounds have anti-microbial activities against different microbial groups, but unfortunately the methanogens donot have any correlation with the methane emitted by the animals.
• The plant secondary metabolites might have anti-protozoal activity, which might indirectly result in reduced numbers of methanogens. As the ciliate protozoa and methanogens have an ecto-symbiotic relationship, the latter might lose their symbiotic partners and hydrogen supply due to killing of ciliates by the plant secondary metabolites and therefore, might result in reduced production of methane (Santra et al., 1994).
• As the plant secondary metabolites have anti-microbial activity, which might reduce the numbers of bacteria and fungi