Greenhouse gas (GHG) emissions from agriculture are a major contributor to climate change. The Stern review 2006 identified that agriculture accounted for ~14 % of GHG with an additional 18% of emissions due to deforestation to provide more agricultural land. In the UK about 7% of GHG is contributed by agriculture (AEA Technology plc, 2007). The main greenhouse gases are nitrous oxide (N2O), methane (CH4) and carbon dioxide (CO2). Of these N2O is ~300 times more potent GHG than CO2 and CH4 is 21 times more potent than CO2. In the UK agriculture is the major contributor to N2O and some 70kt N2O is emitted annually equivalent to 21.7Mt CO2. Enteric fermentation contributes greatly to methane emission and there is evidence that feed compositio...