Nonruminant Nutrition Phytase , What is New and What Needs to be Done ?

The majority of the P in cereal grains and oilseed meals is organically bound as phytic acid or phytate. This form of P is nutritionally unavailable to nonruminant animals due to the lack of phytase in their digestive tract. As a result, swine and poultry diets must be supplemented with highly available, inorganic sources of P to meet their P requirements. The poor bioavailability of P in the natural feedstuffs along with high dietary levels of supplemental P result in higher levels of fecal P compared with ruminant animals. In the early 1970s, research at Arkansas showed that supplementing a chick diet with microbial phytase improved the utilization of P. Studies in the early 1990s at Kentucky and Michigan showed that feeding pigs a low-P, corn-soy diet supplemented with phytase from a mutant strain of Aspergillus niger improved the bioavailability of P. At about the same time, research in the Netherlands and at our station also demonstrated the efficacy of phytase produced by recombinant Aspergillus niger in studies with pigs and chicks. In November, 1995, a commercial source of recombinant-produced phytase (Natuphos r ) was approved for use in the USA. Since then, other sources and forms of phytase have been developed and evaluated. A considerable amount of research has been conducted with phytase. From 1992 to 2001, 82 papers involving phytase were published in Poultry Science (n=55) and the Journal of Animal Science (n=27), with 48 of these published in the last 4 years. The studies clearly show that phytase increases the digestibility and bioavailability of P from phytate, reduces the amount of inorganic P needed to maximize growth and bone mineralization, and markedly reduces fecal excretion of P. Phytase also seems to increase the bioavailability of Ca, Zn, and other divalent cations that otherwise bind to phytate. Some studies suggest that phytase may improve ileal digestibility of amino acids slightly, but other studies have not shown this response. This new technology offers substantial benefits to swine and poultry production by reducing the potential for environmental problems associated with excess P excretion.