Daily CH4 production was high compared to other studies . This was due to the higher DMI and ECM yield in the present study, since CH4 production per kg DMI and per kg ECM was comparable to similar studies. The differences in CH4 production between treatments were in the same range as in similar studies. Polyunsaturated FA are found to be more toxic to rumen microbes than monounsaturated FA and the decreasing effect of fat on CH4 production increases with degree of unsaturation of FA