The hens were fed diets in mash form during the experiment (64–76 weeks of age). The basal diet was formulated (Table 1)according to recommendations of NRC (1994). The basal diet contained 0, 5, 10, 15 or 20 g/kg of dried peppermint leaves,respectively, for five treatment diets. First, the peppermint leaves of different levels were mixed separately in 3 kg of the