The loss of digestible energy from ruminant feeds as methane gas is often assumed to be about 0.08 of gross energy (GE) intake. This represents a significant loss of feed energy and recently concern has been expressed about the importance of methane as a gas which contributes to global warming. As methane is a gaseous loss, its measurement requires specialised equipment. Therefore the metabolisable energy (ME) content of many feedstuffs is estimated using a predicted methane energy loss.