Five dietary treatments were applied in a 35-day trial to evaluate the single and combined effects of phytase and citric acid on growth performance, nutrient digestibility, tibia bone mineralization, intestinal morphology, and blood parameters in growing Japanese quails fed diets with reduced content of nonphytate phosphorous (nPP). On day 1, a total of 500 quail chicks were randomly allotted to 5 treatments with 5 cages of 20 birds for each diet: PC (positive control; adequate amounts of nPP), NC (negative control; 0.12 % reduction in dietary nPP content), PHY (NC + 500 FTU phytase /kg), CA (NC + 30 g citric acid /kg), and PHY + CA (NC + phytase + citric acid). After 35 days, the body weight, average daily gain, and apparent total tract digestibility coefficients (ATTDC) of crude protein in quails fed with any of the diets were higher (P < 0.01) than those in birds fed diet NC, where the birds fed diet PHY + CA had the highest values. Quail chicks fed diets PHY and PHY + CA also had improved overall feed conversion ratio (P = 0.024) and ATTDC of phosphorous (P = 0.005) than those fed diet NC. All diets, except diet PC, resulted in the increased nitrogen-corrected apparent metabolizable energy (AMEn) value and ATTDC of ash and energy (P < 0.05) compared to the NC diet, where the highest AMEn was obtained using the combination of phytase and citric acid. At 35 days of age, quails fed with any of the diets had greater (P < 0.05) tibia diameter, tibia ash content, villus height (in both jejunum and ileum), villus height/crypt depth ratio (in the jejunum), and villus surface area (in the ileum), but lower (P < 0.05) serum alkaline phosphatase activity than those fed diet NC. Feeding diets PC, PHY, and PHY + CA also increased (P < 0.05) tibia phosphorous content and serum concentrations of phosphorous, albumin, and parathyroid hormone (PTH) compared with the NC diet, where quails fed diet PHY + CA had the highest tibia phosphorous content and serum PTH level. Overall, th
