An increase in poultry production in recent years has led to a greater use of poultry manure as fertilizer, which has in turn increased the amount of phosphorus runoff from fields fertilized with poultry manure. Phosphorus excretion in poultry manure can lead to water pollution when manure is used as fertilizer. The need to maintain dietary phosphorus levels while redcuing excretion in poultry manure has led to the increase in the application of phytase to poultry feed in recent years. The use of phytase reduces phosphorus excretion in poultry manure by allowing the birds to utilize more of the phytate phosphorus. Phytate phosphorus has the ability to complex with cations such as calcium, magnesium, zinc, copper, and nitrogen and certain gastrointestinal proteases, thus reducing the availability of these cations and of amino acids. The use of phytase may free these cations and proteases bound in phytata phosphorus complexes and improve production parameters and body structure characteristics in broilers and laying hens, such as body weight, bone ash content, feed consumption, egg weight, and eggshell quality.