Higher animals lack the enzymes to digest cellulose. Since ruminants only feed on grass which contains large quantities of cellulose, an arrangement was provided by nature, where ruminants had to recruit a partner that would help it digest this cellulose and convert it into soluble TCA cycle metabolites. Ruminants have evolved together with bacteria, protozoa etc that have the ability to digest cellulose. This symbiotic relationship entails the presence of bacteria and protozoa in Ruminant forestomach. Bacteria and protozoa ferment their feed (grass) to produce substances referred to as volatile fatty acids. Methane (a green house gas) is a by-product of this fermentation process. So the more ruminants there are the more greenhouse gas produced

Daniyal,

It's all about methanogenesis and there is a lot of information out there on this subject

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The following links should give you enough information to get some answers for your question:

https://www.quora.com/How-does-livestock-produce-methane

https://encyclopedia2.thefreedictionary.com/methanogenesis

http://www.thebeefsite.com/articles/2095/understanding-the-ruminant-animals-digestive-system/

Hope this helps,

Tomas

Thank you for your responses. Really helpful.