Which is a bigger methane source: cow belching or cow flatulence?

Contrary to common belief, it's actually cow belching caused by a process called enteric fermentation that contributes to methane emissions. Enteric fermentation is the digestive process in which sugars are broken down into simpler molecules for absorption into the bloodstream. This process also produces methane as a by-product. However, a small percentage of methane is also produced in the cow's large intestine and released. Additionally, significant amounts of this greenhouse gas are generated in settling ponds and lagoons used for processing cow manure.