It is only recently that the importance of the microbiota in the human gut has being fully appreciated as pivotal to human health. This is surprising, because the colonisation of the guts of ruminant livestock is known to provide essential health effects. That the processes in the human colon resemble those within ruminant livestock suggests that a knowledge of the latter may be of interest to the informed nutritionist. Generally ruminant animals possess bacteria, protozoa and fungi within their rumens. Over 60 species of bacteria are known with total bacteria counts equating to between one billion to ten billion organism per mL. Most bacteria in ruminant livestock are non spore forming anaerobes whose main function is the fermentation of cellulose into short chain fatty acids such as butyric, acetic and propionic acid which is then absorbed and used as a source of energy by the animal. Such production of short chain fatty acids is now known to provide substantial energy to humans and may provide up to 5 % of total energy needs.
As well as bacteria, the rumen also contains a lesser number of protozoa (upto 1 million organisms per mL). However, as the protozoa are larger than the bacteria size, the total mass may be similar. Most of the protozoa and ciliates belonging to the holotrich or oligotrich groups. The protozoans belonging to the oligotrichs can ingest food particles, but unlike holotrichous protozoa and bacteria, they cannot ferment cellulose to produce short chain fatty acids. Less is known about the fungi of the rumen which constitute around 10 percent of the microbial biomass. However, as with the bacteria, they are strictly anaerobic and their life cycles include a motile phase as a zoospore and a non-motile phase as a sporangium. As sporangia, they become attached to food particles by rhizoids which penetrate the cells walls where they digest most carbohydrates. The bacteria, protozoa and fungi work as a consorti within the rumen, with fungi invading the plant tissue and the protozoa and bacteria fermenting the product of this invasion. Around 20 % of the nutrients required by ruminants are provided by its microflora and fauna.