Biological Phenomena

Ruminal Methanogesis

1) Cattle are responsible for significant release of methane. Less known are the methods of this mechanism. The stomach of ruminants is composed of several chambers in front of the abomasums, which fulfil the function of breaking down the introduced nutrients. The rumen (= the paunch) is the first of these chambers and plays a main function in the digestion, since 70% of the process happens here. The rumen, just like the other digestive chambers, is inhabited by a multiplicity of micro-organisms (bacteria, archaea, fungi, etc) which take part in the process of digestion. However, these microorganisms are also responsible for the production of methane that is later released.

Mechanisms

Food ingested by the animal remains between 20 and 70 hours in the rumen, where it is broken down manually. Polysaccharides contained in the (plant) food of animals, such as cellulose, starch or pectin are transformed (by degradation) into simpler and smaller units, bolus. Their fermentation is then used to create volatile fatty acids, CO2, and hydrogen. Later on, this hydrogen will be used by micro-organisms for the production of methane (CH4). The formation of certain fatty acids is a creator of hydrogen (acetate) while the other acids (pyruvate, butyrate) are consumers.

CO2 + H2 –> CH4 + H2O

All these fermentation reactions produce energy in the form of TPA molecules (Tri-Phosphorus Acid), energy that will be used by microorganisms for the formation of cellular elements which will eventually make up the source of the animal’s amino acids (up to 50-90%).
However, since the rumen is an anaerobic environment, the formation of TPA by oxidation requires the production of metabolic hydrogen (2H). In very high concentration, this hydrogen inhibits the oxidation reactions (which lead to the formation of TPA) And without TPA there is no energy, which ultimately leads to a very serious dysfunction in the metabolism of the animal. The presence of this metabolic hydrogen is thus important, but not in large quantities. 
Thus, methanogenesis is an important and essential phenomenon in the digestive process of a ruminant. The produced methane is then released into the environment at approximately 500 L per day per adult cattle. This release is accomplished 95% orally.

Environmental Impact

Methane is regularly singled out when it comes to discussing the factors of air pollution. Methane (CH4) has a much higher risk than carbon dioxide (CO2) since when comparing equal weights of the gases, methane is almost twenty times more polluting. Although less present in the atmosphere, the responsibility of methane in the global greenhouse effect is considered to be at around 20%. 
The participation of ruminants in the release of methane into the atmosphere is estimated at 3% of global methane, much less than the contribution of wetlands or peat bogs, rice plantations, or certain green plants in the natural environment (KEPPLER et al., 20062)).

Tonnes/year (M=million(s)) French Herbivores French Cattle World Herbivores Green Plants
Amount of Methane Liberated 1,45 M 1,32 M 80 M 62-236 M

1) Presented with a help of: MARTIN C., MORGAVI D., DOREAU M., JOUANY J.P. (2006). Comment réduire la production de méthane chez les ruminants ? Fourrages, 187, 283-300.
2) KEPPLER F., HAMILTON J.T.G., BRAB M., RÖCKMANN T. (2006). Methane emissions from terrestrial plants under aerobic conditions. Nature, 439, 187-191.

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