The present invention provides an isolated animal cell comprising an exogenous nucleic acid encoding a mutated phytase, wherein the cell produces phytase and secretes the phytase from the cell. The present invention also provides an animal having a phenotype not naturally occurring, characterized by secretion of phytase into the lumen of the gastrointestinal tract of the animal, the phenotype being conferred by a transgene contained in the cells of the animal, the transgene comprising a nucleic acid sequence encoding phytase and methods of making said animal.