JOURNAL OF ANIMAL SCIENCE

In feedstuffs of plant origin, phosphorus is present in both organic and inorganic forms. Most of the organic phos-phorus in plant ingredients is bound to complex struc-tures called phytate (myo-inositol hexakisphosphate), which is the mixed salt of phytate [1]. Phytases hydrolyze phosphomonoester bonds of phytate, which releases bound phosphorus and produces lower forms of myo-in-ositol phosphates [2]. However, digestion of phytate is limited in pigs due to insufficient production of en-dogenous gastric or intestinal phytases [3,4]. Phytate also has the ability to form calcium-phytate complexes, which renders calcium unavailable for absorption [5,6]. However, adding exogenous phytases to swine and poultry diets improves phosphorus and calcium digest-ibility and reduces phosphorus excretion [7-9]; and thus, phytase use has become a routine practice. Conse-quently, exogenous phytases are being developed through genetic engineering based on the gene se-quences and protein structures of phytase. The threeFerdinando Nielsen Almeida, Rommel Casilda Sulabo and Hans Henrik Stei