The CRF sector (IPCC 2006) 'enteric fermentation' is an agriculture, forestry and land use sector defined by the 2006 IPCC Guidelines for National Greenhouse Gas Inventories:
Methane emissions from herbivores as a by-product of enteric fermentation (a digestive process by which carbohydrates are broken down by micro-organisms into simple molecules for absorption into the bloodstream). Ruminant animals (e.g., cattle, sheep) are major sources with moderate amounts produced from non-ruminant animals (e.g., pigs, horses).