The three dietary treatments were control (basal diet without shiitake mushroom), and diets containing 0.25 and 0.5% shiitake mushroom. The basal diet was formulated (Table 1) to meet or exceed nutrient requirements of laying hens (NRC, 1994). The shiitake strain used in the experiment was L. edodes KFRI 405, which was maintained at the Korea Forest Research Institute (KFRI), Seoul, Korea. All parts of the mushrooms were air-dried and then ground to a fine powder using an electric blender.