Monogastric organisms contained no or only negligible amount of endogenous phytase in the stomach and small intestine, these animals are therefore dependent on plant or microbial phytase (Pallauf and Rimbak, 1997).The positive response for laying hens fed unsupplemented mash basal diet containing 15% wheat bran revealed that native phytase from plant source could not be totally neglected if the diet was in mash form. It has been reported that hydrolysis of phytate within the digestive tract of poultry may be attributed to the action of phytase from one of three possible sources namely plant feed ingredients, animal-intrinsic phytase activities and microbial origin (commercial) phytase product (Ravindran et al., 1995). However, pelleting the basal diet adversely affected the potency of the native wheat bran phytase as the feed conversion of laying hens fed unsupplemented pelleted basal diet (T2) was poorer when compared to those fed unsupplemented mash basal diet (T1). Inactivation of the wheat bran phytase may be reason for the poor feed conversion. This finding is in consonance with the report of Cavalcanti and Behnke (2004) that heat treatment destroys phytase. Ullah and Mullaney (1996) also stated that losses in activity of phytase enzyme begin to occur when feeds are subjected to steam pelleting around 600C.