Methane production by ruminants

Methane is produced from carbon dioxide and hydrogen as a by-product of rumen fermentation. Excess hydrogen is produced together with the production of acetate and butyrate but not with the production of propionate and valerate. Diets lower in fibre and higher in starch result in higher proportions of propionate in the rumen volatile fatty acids and less methane per mole of substrate fermented. There is significant variation between animals in methane production. Research is underway to refine methane emissions factors for different classes of livestock. Smaller amounts of methane are also produced in the hind gut and from manure.