Efficacy of different levels of Escherichia coli phytase in broiler diets with a reduced P content.

Escherichia coli-derived 6-phytase expressed in Pichia pastoris (Optiphos) was added to broiler rations with considerably reduced levels of phosphorus (by 1.5 g/kg). This experiment, performed over a five-week period, involved Ross 308 male chickens kept in battery cages. Each group was divided into 9 subgroups, each of 9 chickens (81 birds per treatment). Birds were allocated to a positive control group (I), a negative control group (II) and three phytase-supplemented groups (III-V--the diet as in group II + 250, 500 and 750 FTU Escherichia coli phytase/kg feed, respectively). The major components of starter and grower diets were corn, soybean and wheat meals. Starter and grower diets (in meal form) contained 6.73 and 6.05 g total P/kg, 4.05 and 3.46 g available P (aP)/kg, respectively, in group I, and 5.23 and 4.55 total P/kg, 2.54 g and 1.95 g aP /kg, respectively, in groups II-V. Phytase efficacy was evaluated based on performance results, carcass quality and bone mineralization. P reduction in group II decreased weight gains by 9.1% and increased feed conversion by approximately 8.4%, compared with group I. Diet supplementation with phytase in groups IV and V significantly compensated for the decrease in performance observed in group II. The differences in dressing percentage between group II and groups III and V were significant. Phosphorus reduction in the diets negatively influenced the process of bone mineralization, which was enhanced by phytase supplementation.