In the ruminant stomach as in of cattle and sheep each ml of fluid in the rumen (anterior stomach) contains up to a million ciliate protozoa of many species, mostly entodiniomorphs and trichostomes. The ciliates are anaerobes tolerating low levels of oxygen. The entodiniomorphs ingest and break down plant fragments and both trichostomes and bacteria take up sugars from the gut contents; carbohydrates are fermented by the symbionts and the volatile fatty acids released provide two thirds of the dietary energy of the host, the cellulolytic and amylolytic activities of ciliates prolong fermentation processes and produce perhaps one third of the volatile fatty acids. The ciliates contain hydrogenosomes producing hydrogen which either reacts with oxygen or is used by methanogenic bacteria. The microbes including the ciliate protozoa ferment and break down plant cell walls into their carbohydrate fractions and produce volatile fatty acids (VFAs), such as acetate (used for fat synthesis), priopionate (used for glucose synthesis), and butyrate from these carbohydrates. The animal later uses these VFAs for energy.