Methanogens are a group of microorganisms that produce methane as a byproduct of their metabolism.
The digestive tract of ruminants contains four major parts: rumen, reticulum, omasum and abomasum.
The majority of anaerobic microbes assisting the cellulose breakdown occupy the rumen and initiate the fermentation process.
The animal absorbs the fatty acids, vitamins and nutrient content on passing the partially digested food from the rumen to the omasum.
This decreases the pH level and initiates the release of enzymes for further breakdown of the food which later passes to the abomasum to absorb remaining nutrients before excretion.