Calcium and phosphorus digestibility in broilers as affected by varying phytate concentrations from corn

Dietary phytate P (PP) concentration impacts Ca and P digestibility in broilers. Research was conducted to determine the impact of increasing concentration of dietary PP, with and without phytase, on broiler standardized ileal digestibility (SID) of Ca and P. Digestible (Dig) Ca and P were calculated by multiplying SID and the analyzed dietary Ca and P concentrations. The experiment was a factorial arrangement of 2 phytase (0 and 1,000 U/kg) and 4 PP (0.16, 0.23, 0.29, and 0.34%) concentrations. Treatments were fed for 36 h from 20 to 22 d of age (4 b/pen, n ≥ 7 replicate pens/treatment). Different ratios of corn and corn germ were used to achieve the desired PP concentrations. A limestone with 800 µm geometric mean diameter was used as the sole Ca source to achieve 0.7% Ca in the final diets (96% Ca from limestone). An additional diet was fed that was N, Ca- and P-free, for the determination of endogenous losses of each nutrient. Distal ileal digesta were pooled from all birds in a pen. There were no interactions between PP and phytase on SID Ca or Dig Ca from limestone. Irrespective of phytase inclusion, increasing PP from 0.16 to 0.34% decreased SID Ca from 53.8 to 38.1% (P < 0.05). The SID Ca averaged 41.5 and 51.4% in diets containing 0 and 1000 U phytase/kg, respectively, across all PP concentrations (P < 0.05). Interactions were seen between PP and phytase on SID and Dig P (P < 0.05) with SID P of 31.1, 24.0, 20.1, and 16.3% for broilers fed 0.16, 0.23, 0.29, and 0.34% PP diets without phytase, respectively. When phytase was included at 1000 U/kg, SID P was 89.9, 87.5, 73.9 and 60.4% for diets containing 0.16, 0.23, 0.29 and 0.34% PP, respectively (P < 0.05). Overall, phytase improved SID Ca and P independent of PP concentration. However, with increasing PP concentration, both SID Ca and P were negatively affected.