Rumen Health Technical Guide

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Rumen Microflora

The rumen hosts a very diverse community called the microbiota (Bacteria, Protozoa, Fungi) 2ReferenceView allChaucheyras-Durand F., Ossa F.
The rumen microbiome: composition, abundance, diversity and new investigative tools. Prof Anim Sci. 2014; 30:1-12.
10ReferenceView allMcSweeney C.S., and Mackie R.I. 2012.
Micro-organisms and ruminant digestion: State of knowledge, trends and future prospects. Commision on Genetic Resources for Food and Agriculture. Background study paper No.61.
11ReferenceView allMorgavi D.P., Kelly W.J., Janssen P.H., and Atwood G.T. 2012.
Rumen microbial (meta)genomics and its application to ruminant production. Animal. 1:1-18.


Rumen bacteria account for 1010 organism/mL of rumen fluid and several hundred species have been characterized to date. By volume, they comprise up to 50% of the total microbial biomass. Bacteria species are an important source of microbial protein, which supply the ruminant with 75-80% of its metabolizable protein. Bacteria are also important for producing enzymes that digest fiber (cellulose, hemicellulose), starch and sugars.



Ciliate protozoa are organisms larger than bacteria and account for 10organisms / mL of rumen fluid, however they still make up to 50% of the total microbial biomass. They have various activities:

  • Cellulolytic and hemicellulolytic can digest plant particles
  • Different protozoa have a positive role digesting starch (more slowly than bacteria)
  • Others protozoa can consume lactic acid, thereby limiting the risk of acidosis
  • Some types of protozoa are able to remove oxygen so they have a stabilizing effect upon anaerobiosis.

However, most of them degrade proteins very efficiently and release ammonia, so they can waste dietary protein. These proteins represent around 25% of the microbial protein available for the animal. Ciliate protozoa produce large amounts of hydrogen, which is a substrate for methanogens. The ciliate species are predators of other rumen microbes. In fact, a single protozoal cell can swallow up to several thousand bacteria in an hour so they play a very important role in rumen microbial population stability.




Rumen fungi comprise up to 8-10% of microbial biomass and are strictly anaerobic. They play an essential role in fiber digestion due to the production of filamentous rhizoids which invade plant tissues, and their efficient enzymatic activities. This physical action to plant cell walls, can facilitate access to more digestible tissues and help release polysaccharides, which are linked to lignin increasing the pool of digestible energy for the rumen microflora.