Extra-phosphoric effects of phytase with and without xylanase in corn-soybean meal-based diets fed to broilers.

Two experiments were conducted to evaluate the extra-phosphoric effects of phytase on amino acid (AA) and energy digestibility (experiments 1 and 2) and growth performance (experiment 2) of broilers fed diets adequate in Ca and nonphytate P supplemented with xylanase. Ross × Ross 708 broiler chicks (864 males in experiment 1 and 1,152 females in experiment 2) were randomly distributed into battery cages (6 replicate cages per treatment) with 12 birds per cage at 1 d of age. In both experiments, factorial arrangements of treatments were evaluated consisting of 6 phytase [0, 1,000, 2,000, 4,000, 8,000, or 16,000 phytase units (FTU)/kg] and 2 xylanase [0 or 16,000 birch xylan units (BXU)/kg] concentrations in experiment 1 and 4 phytase (0, 500, 1,000 or 2,000 FTU/kg) and 4 xylanase (0, 8,000, 16,000, or 32,000 BXU/kg) concentrations in experiment 2. Treatments were provided from 27 to 32 d of age in experiment 1 and from 1 to 32 d of age in experiment 2. Digesta contents of the terminal ileum were collected at 32 d of age (experiment 1 and 2), and growth performance was measured at 1, 14, and 25 d of age in experiment 2. There was no interaction of phytase and xylanase; only main effects of phytase were observed. In experiment 1, broilers fed diets supplemented with phytase at 1,000 FTU/kg had increased (P < 0.05) apparent ileal digestibility (AID) of all AA with the exception of Ala and Met. Diets fed to broilers supplemented with higher concentrations of phytase did not further increase AID of any AA (P > 0.05) above the addition of 1,000 FTU/kg of phytase. Phytase supplementation did not affect ileal digestible energy (P > 0.05). For all variables measured, significant log-linear or log-quadratic effects of phytase (P > 0.05) were not observed. In contrast, broilers fed diets supplemented with phytase in experiment 2 exhibited log-linear (P < 0.05) increases in AID of AA but not apparent ileal digestible energy. However, supplementation with 2,000 FTU/kg of phytase increased (P = 0.05) ileal digestible energy by 36 kcal/kg compared with the basal diet. Broilers fed diets with 1,000 FTU/kg of phytase had improved growth performance (P < 0.05) in comparison with broilers fed diets containing 0 or 500 FTU/kg of phytase. The addition of 500 FTU/kg of phytase in diets fed to broilers did not affect ileal digestibility or growth performance (P > 0.05). Data obtained from these experiments demonstrated extra-phosphoric effects in broilers fed diets supplemented with 1,000 FTU/kg of phytase and diminishing returns with higher concentrations.