Corn expressing an Escherichia coli-derived phytase gene:: Comparative evaluation study in broiler chicks

The efficacy of corn expressing an Escherichia coli-derived gene (corn-based phytase; CBP) and an E. coli-derived microbial phytase (expressed in Pichia pastoris) sprayed onto a wheat carrier (Quantum) was comparatively evaluated in two 14-d broiler chicken studies. In experiment 1, a total of 288 seven-dayold male broiler chicks were grouped by weight into 8 blocks of 6 cages, with 6 birds per cage, and used to measure growth performance, bone mineralization, and nutrient utilization. In experiment 2, a total of 192 seven-day-old male broiler chicks were used, with 4 birds per cage. Six dietary treatment groups were randomly allotted to the cages within each of 8 blocks. The cornsoybean meal-based diets used in each study consisted of a positive control adequate in P and Ca; a negative control (NC) low in P and Ca (no added inorganic P); the NC supplemented with 3,630, 36,300, or 363,000 phytase units (FTU) of CBP/kg; and the NC + 3,630 FTU of Quantum/kg. Growth performance and bone mineralization criteria were reevaluated in the second broiler study. Data from the 2 experiments were combined because there was no diet x experiment interaction and analyzed as a randomized complete block design. Weight gain decreased (P < 0.05) with a reduction in dietary P and Ca in the NC diet. Weight gain, feed efficiency, and percentage of tibia ash of birds fed 3,630 FTU/kg of either CBP or Quantum phytase were not different. There was a quadratic response (P < 0.01) to CBP supplementation of the NC diets in weight gain of the broiler chicks. Feed intake increased quadratically (P < 0.01) with CBP supplementation of the NC diets, but CBP supplementation of the NC diets did not affect feed efficiency. Tibia ash of birds fed the positive control diet was greater (P < 0.01) than that of birds fed the NC diet. There was a quadratic response (P < 0.01) to CBP supplementation of the NC diets in tibia ash of the broiler chicks. Birds fed supplemental phytase had greater (P < 0.01) ileal and total tract P and Ca digestibility than birds fed the NC diet. Data from the study suggest that E. coli phytase expressed in corn is efficacious in P-deficient broiler chick diets for the improvement of growth performance and indices of P utilization, which would minimize the need for supplemental P in broiler diets.