Enteric fermentation
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. Because of human agricultural reliance in many parts of the world on animals which digest by enteric fermentation, it is the second largest anthropogenic factor for the increase in methane emissions directly after fossil fuel use. Ruminant animals are those that have a rumen. A rumen is a multichambered stomach found almost exclusively among some artiodactyl mammals, such as cattle, sheep, and deer, enabling them to eat cellulose-enhanced tough plants and grains that monogastric (i.e., "single-chambered stomached") animals, such as humans, dogs, and cats, cannot digest. Although camels are thought to be ruminants they are not true ruminants. 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 belched 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. However, in Australia there are ruminant species of the kangaroos that are able to produce 80% less methane than cows.
