An experiment was conducted to investigate the effect of dietary non-phytate phosphorus (NPP) level on growth performance, bone characteristics and phosphorus metabolism-related gene expressions, to evaluate the dietary NPP requirement of broiler chicks fed a conventional corn-soybean meal diet from 1 to 21 d of age. A total of 540 day-old Arbor Acres male chicks were randomly allocated to one of nine treatments with six replicate cages of 10 birds per cage in a completely randomized design, and fed a basal corn-soybean meal diet (containing 0.08% of NPP) supplemented with 0.10, 0.15, 0.25, 0.30, 0.35, 0.40, 0.45, or 0.50% of inorganic phosphorus in the form of CaHPO4•2H2O, respectively. Each diet contained the constant calcium content of about 1.0%.

The results showed that daily weight gain, serum inorganic P, tibia bone strength, tibia ash percentage, tibia bone mineral content (BMC) and density (BMD), middle toe ash percentage, middle toe BMC and BMD were affected (P ‹ 0.0001) by dietary NPP level, and increased linearly (P ‹ 0.0001) and quadraticly (P ‹ 0.004) as dietary NPP levels increased. The gene expression of type IIb sodium-phosphate cotransporter (NaPi-IIb) in the duodenum was affected (P ‹ 0.03) and decreased linearly (P ‹ 0.002) as dietary NPP levels increased. Dietary NPP requirements estimated based on fitted broken-line models (P ‹ 0.0001) of the sensitive indices including daily weight gain, tibia bone strength, tibia ash percentage, tibia BMC and BMD as well as middle toe ash percentage were 0.34–0.39%. The results from this study indicate that tibia BMC and BMD might be new, sensitive, and noninvasive criteria to evaluate the dietary NPP requirements of broilers, and the dietary NPP requirement is 0.39% for broiler chicks fed a conventional corn-soybean meal diet from 1 to 21 d of age.