An experiment was carried out on 30 Black-and-White Lowland bulls fattened from 165 to 485 kg BW, divided into three groups fed diets without evening primrose oil cake (control group C) or with a contribution of 10 (group P1) or 30% (group P2) of evening primrose cake. Bull performance, nutrient digestibility, nitrogen balance, ammonia and volatile fatty acids in the rumen fluid, physicochemical properties of meat and subcutaneous and kidney fat composition were estimated. Average daily body gain was 1333 g in group P1; 1235 g in P2; and 1216 g in C. The content of oleic (C_18:1) and linoleic (C_{18:2 n6}) acid in subcutaneous and kidney fat was higher in bulls fed diets with evening primrose oil cake than in controls.