Methane emission from ruminant livestock is currently estimated to be around 100 million tonnes of methane each year and, after fossil fuel-related emissions, represents the biggest man-made methane source.

The loss of methane from ruminant livestock is a problem not only in the respect of greenhouse gas emissions, but also to farmers in that food converted into and released as methane is food not being converted into meat and/or milk.

Methane is produced in the guts of ruminant livestock as a result of methanogenic microorganisms (belonging to the Archaea). The composition of the animal feed is a crucial factor in controlling the amounts of methane produced, but a sheep can produce about 30 litres of methane each day and a dairy cow up to about 200.

Human Impact

As with rice agriculture, methane emission arising from ruminant livestock is, by definition, entirely due to man. With a continuing expansion of meat and dairy product consumption around the world, the demand for ruminant livestock and so the size of this methane source has grown rapidly.

Intensive rearing methods, developed to provide large amounts of meat and dairy products at low prices and to a wide consumer base, has led to very high densities of ruminant livestock and strong local methane sources. An additional, but important, source of methane due to ruminant livestock is that of animal waste and this aspect is discussed in the 'Methane Sources - Waste' section.

Potential for control

The best studied and applied methane reduction strategy has been that of altering the feed composition, either to reduce the percentage which is converted into methane or to improve the meat and milk yield. Improvements in the overall quality of animal feed may allow meat and dairy production to be maintained at the same level with fewer animals and so less total methane emission.

Relatively recent ruminant methane reduction strategies have included the introduction of methane inhibitors, both biological and chemical, with the animal feed, to kill off or at least reduce the activity of the methanogenic microorganisms in the gut.