Because ruminants make a significant contribution to greenhouse gas emissions, attempts are being made by dietary manipulation, to mitigate methane emissions without altering animal performance. Dietary fat supply may be a promising solution (Martin et al., 2008a). A first experiment has shown that increasing extruded linseed supply in a hay-based diet resulted in a decrease in methane production (Martin et al., 2007). A second experiment has been carried out using a maize silage-based diet and the same linseed supply. The present abstract summarises the results of both experiments.