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Enteric fermentation is a digestive process by which carbohydrates are broken down by microorganisms into simple molecules for absorption into the bloodstream of an animal. Food and Agriculture Organization (FAO) estimated that ruminant livestock contribute to around 34.5 percent of the total anthropogenic methane emissions.
Enteric fermentation occurs when methane (CH4) is produced in the rumen as microbial fermentation takes place. Over 200 species of microorganisms are present in the rumen, although only about 10% of these play an important role in digestion. Most of the CH4 byproduct is by the animal. However, a small percentage of CH4 is also produced in the large intestine and passed out as flatulence.
Methane emissions are an important contribution to global greenhouse gas emissions. The IPCC reports that methane is more than twenty times as effective as CO2 at trapping heat in the atmosphere - though note that it is produced in substantially smaller amounts. Methane represents also a significant energy loss to the animal ranging from 2 to 12% of gross energy intake. So, decreasing the production of enteric CH4 from ruminants without altering animal production is desirable both as a strategy to reduce global greenhouse gas emissions and as a means of improving feed conversion efficiency. In Australia ruminant animals account for over half of their green house gas contribution from methane.Australian Greenhouse Office, "National Greenhouse Gas Inventory", Canberra ACT, March 2007.
However, in Australia there are ruminant species of the kangaroos that are able to produce 80% less methane than cows. This is because the gut microbiota of Macropodids, rumen and others parts of their digestive system, is dominated by bacteria of the family Succinivibrionaceae. These bacteria are able to produce Succinic acid as a final product of the lignocelluloses degradation, producing small amounts of methane as end product. Its special metabolic route allows it to utilize other proton acceptors, avoiding the formation of methane.
Recent studies claim that this technique is possible to perform. In one of these studies scientists analyze the changes of human microbiota by different alimentary changes. In other study, researchers introduce a human microbiota in gnotobiotic mice in order to compare the different changes for developing new ways to manipulate the properties of the microbiota so as to prevent or treat various diseases.
Another approach to manage methane emissions from enteric fermentation involves using diet additives and supplements in cattle feed. For example, Asparagopsis taxiformis (also known as red seaweed) is a species of algae that when fed to cattle has shown to substantially reduce their methane emissions in . A second example that has been shown to reduce methane emissions from cattle significantly in feedlots involves using the compound 3-nitroxypropanol (3-NOP) which inhibits the final step of methane synthesis by microorganisms in the rumen. Some of these methods have already been approved for farmer usage, while others continue to be evaluated for safety, efficacy, and other concerns. These approaches comes with limitations as feedlot emissions represent around 11% of overall cattle emissions.
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