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Evaluation of a Microbial Phytase, Produced by Solid-State Fermentation, in Broiler Diets. 1. Influence on Performance, Toe Ash Contents, and Phosphorus Equivalency Estimates

Y. B. Wu^*, V. Ravindran^*, P. C. H. Morel^*, W. H. Hendriks^* and J. Pierce

^* Institute of Food, Nutrition and Human Health, Massey University, Palmerston North, 5301, New Zealand
Alltech Biotechnology Center, Alltech, Inc., 3031 Catnip Hill Pike, Nicholasville, Kentucky 40356

Correspondence: V. Ravindran, E-mail: V.Ravindran{at}massey.ac.nz

The influence of graded additions of a microbial phytase, produced by solid-state fermentation, on the performance and toe ash contents of male and female broilers fed a wheat-soy-canola diet was investigated in a 42-d trial. Responses to graded levels of inorganic phosphorus were also evaluated to calculate the equivalency values of the phytase for inorganic phosphorus. Weight gains, feed per gain, and toe ash contents were increased as the inorganic phosphorus or phytase was added to the low-phosphorus diet. The magnitude of increment in these parameters was greatest for the first addition of inorganic phosphorus or phytase and then tended to plateau with further additions. Weight gain and toe ash content of birds fed the low-P diet with 500 phytase units (PU)/kg of diet were similar to those of birds fed the adequate-P diet, but the feed efficiency was 1.6 to 3.3% better. In general, the treatment effects on parameters tested were similar in both sexes. Spurious phosphorus equivalency values, translating into phosphorus release values of 72 to 137% from phytate-phosphorus, were obtained for this phytase product. These findings highlight the limitations of employing conventional methods to determine equivalency values for a microbial phytase product that contains side-enzyme activities.

Key Words: broiler • microbial phytase • performance • phosphorus equivalency