LAUSR

An experiment was conducted to evaluate graded doses of phytase in high-phytate diets. Ross 308, male broilers (n = 600) were assigned to one of 4 diets, with 10 replicate pens/diet and 15 birds/replicate pen. Diets were a nutrient adequate positive control (PC), a negative control (NC) diet with a reduction of Ca by 0.22%, available P by 0.20%, energy by 120 kcal/kg, and amino acids by 1 to 5% compared with the PC. The NC diet was supplemented with 0, 2,000, or 4,000 phytase units (FTU)/kg. Phytase increased (linear, P < 0.05) weight gain from hatch to day 18. Birds fed the NC + 4000 FTU/kg ate and gained more (P < 0.05) than birds fed the PC. The apparent ileal digestibility (AID) of all nutrients and amino acids were reduced (P < 0.05) in birds fed the NC compared with birds fed the PC. Phytase increased (linear, P < 0.10) AID of most nutrients. Digestibility was lower (P < 0.10) in birds fed the NC + 4000 FTU/kg compared with birds fed the PC. Using daily intake and AID to determine digestible nutrient intake resulted in no differences between birds fed the PC or NC + 4000 FTU/kg diets. Digestible intake of methionine or glutamate was better correlated with BW gain (P < 0.0001) than AID (P > 0.10). Phytase reduced (linear, P < 0.01) phytate concentration and increased inositol (linear, P < 0.01), phytate hydrolysis (linear, P < 0.05), and jejunal expression (linear, P < 0.05) of SNAT-1 and LAT-4 transporters. Supplementation of increasing doses of phytase in high-phytate, low-nutrient dense diets improved gain and digestibility through nearly complete phytate destruction. Digestible nutrient intake may be a better indication of broiler gain than AID alone.