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 (InsP6) concentration and added phytase on gastrointestinal InsP6 degradation, prececal digestibility of P, Ca, and amino acids (AA), and MEN in broiler chickens. Dietary InsP6 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 InsP6-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. InsP6 disappearance in the crop decreased with increasing ORL (45 to 24 %; P = 0.001). Prececal InsP6 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 InsP6 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 InsP6 disappearance relative to FTU was regressed against dietary InsP6, the relationship was non-linear at 500 FTU/kg but linear at 1,500 and 3,000 FTU/kg. Cecal InsP6 concentration increased with ORL and decreased with phytase (P < 0.001). Except for cysteine, prececal digestibility of all AA and MEN decreased with increasing ORL. The data indicated that phytase supplemented at or above 1,500 FTU/kg did not limit gastrointestinal InsP6 degradation and AA digestibility at high InsP6 concentrations of the feed.