Methanogenesis is the main means of disposal of hydrogen in the rumen. Its formation represents a substantial loss of energy to the animal, and it is also the main source of greenhouse gas emissions from agriculture (Moss, 1993). Inhibition of methane production by ruminants would therefore have significant econimic and environmental benefits.
One possible way to decrease methane formation in the rumen is to promote alternative metabolic pathways to dispose of the reducing power, competing with methanogenesis for the hydrogen uptake. Methane production by mixed rumen bacteria was decreased for short periods in vitro when fumarate was added to the medium (Demeyer & Henderickx, 1967). Fumarate is a metabolic precursor of propionate, and it is reduced to succinate by fumarate reductase. In the present experiment longer-term effects of fumarate supplementation on methane production were investigated by the rumen simulation technique (Rusitec).