Interactions between dietary phytate concentration and phytase level on phytate degradation and amino acid digestibility in broiler chickens.

The objective of the present study was to investigate the effects of dietary myo-inositol hexakisphosphate (InsP) concentration and added phytase on gastrointestinal InsP degradation, prececal digestibility of P, Ca, and amino acids (AA), and ME in broiler chickens. Dietary InsP was increased by graded substitution of corn starch with a mixture of 50 % soybean meal, 20 % rapeseed meal, 20 % sunflower meal, and 10 % rice bran (oilseed meal-rice bran level (ORL)). The experiment was arranged in a 4 × 3-factorial design with 4 ORL (leading to 1.4, 1.9, 2.4, and 3.0 g InsP-P/kg) and 3 phytase levels (500, 1,500, and 3,000 FTU/kg). Male Ross 308 broilers were allocated to 84 metabolism units in groups of 10 and assigned to 1 of the 12 diets. InsP disappearance in the crop decreased with increasing ORL (45 to 24 %; P = 0.001). Prececal InsP disappearance and P digestibility linearly decreased with increasing ORL at 500 FTU/kg (83 to 56 % and 80 to 62 %; P < 0.001). Minor differences were determined for prececal InsP disappearance and P digestibility among ORL at 1,500 and 3,000 FTU/kg, but values decreased with increasing ORL (91 to 83 % and 87 to 81 %, respectively; P < 0.001). When prececal InsP disappearance relative to FTU was regressed against dietary InsP, the relationship was non-linear at 500 FTU/kg but linear at 1,500 and 3,000 FTU/kg. Cecal InsP concentration increased with ORL and decreased with phytase (P < 0.001). Except for cysteine, prececal digestibility of all AA and ME decreased with increasing ORL. The data indicated that phytase supplemented at or above 1,500 FTU/kg did not limit gastrointestinal InsP degradation and AA digestibility at high InsP concentrations of the feed.