This study was conducted to investigate the effects of phytase (Phy), benzoic acid (BA) and their interactions on growth performance, nutrients digestibility and tibia mineralization in broiler chickens fed standard or nutrient,s deficient diets. A total of 768 one-d-old male chicks were divided into 8 treatments for 42 d. The treatments were as follows: positive control (PC), PC diet with 0.5 g/kg of BA, PC diet with 500 FTU/kg of Phy, PC diet with 0.5 g/kg of BA and 500 FTU/kg of Phy, negative control diet (NC) with a nutrient deficiency (ND) equal to matrix value of 500 FTU/kg of Phy, NC diet with 0.5 g/kg of BA, NC diet with 500 FTU/kg of Phy, and NC diet with 0.5 g/kg of BA and 500 FTU/kg of Phy. Broiler chickens received NC diets had lower body weight gain (BWG), feed intake (FI) and higher feed conversion ratio (FCR) in the entire experiment (P ≤ 0.05). Dietary ND negatively influenced tibia and toe ash contents, serum, and tibia P contents as well as ileal P, Ca and CP digestibility at d 28 (P ≤ 0.05). FCR of d 1 to 11 and d 12 to 24 improved when Phy was added to NC rather than PC diets (P ≤ 0.05). Phy supplementation did not affect serum P and Ca content at d 28 (P> 0.05), but reduced serum alkaline phosphatase content in broiler chickens fed PC diets (P ≤ 0.05). Phy supplementation increased tibia and toe ash contents at d 28, especially in broiler chickens fed NC diets (P ≤ 0.05). Inclusion of BA did not influence (P> 0.05) tibia ash, tibia Ca and P contents at d 28, but increased toe ash content (P ≤ 0.05).The interaction between BA and the dietary nutrient level was significant for FCR of d 25–42 and d 1–42 (P ≤0.05). Broiler chickens fed PC diets with BA had better FCR compared with those fed PC diets without BA at d 25–42 (P ≤0.05). Adding Phy to the diets containing BA improved BWG and FI at d 1–11(P≤0.05). In conclusion, Phy was effective in improving some growth performance traits, and bone mineralization especially when added to NC diets. However, BA had a positive effect on FCR of broiler chickens fed PC diets and had no impact on ileal nutrients digestibility, but improved toe ash content.
