Enteric fermentation in ruminants is an important source of methane (CH4) production. In the UK, ruminants contribute approximately 20% of all CH4 emission, with most arising from cattle. This presents a considerable challenge for the dairy industry in the battle against global warming, and reduced CH4 emission is likely to be a major target for government policy within the next few years. The objectives of the present study were to evaluate the effects of level of concentrate supplementation and cross-breeding of Holstein cows with Jersey sires on CH4 production.