A total of 288 32-wk-old Lohmann Selected Leghorn (LSL-Lite) laying hens were fed oncorn-soyabean meal-based diets containing three concentrations of rice bran (RB; 0, 75 and150 g/kg; equivalent to 1.8, 2.7 and 3.5 g/kg phytate phosphorus), two of non-phytate phos-phorus (NPP; 2.5 and 3.5 g/kg) and two of microbial phytase (Phyzyme® XP 5000G; 0 and150 FTU/kg) in a 10-wk trial under high temperature condition. The average minimum andmaximum room temperatures were 26.0 ± 1.9 and 36.0 ± 1.8◦C, respectively, with relativehumidity ranging from 42.3 ± 1.8% to 55.1 ± 2.1%. Each dietary treatment was fed to fourcages (six birds/cage) from 32 to 42 wk of age. Egg production, egg weight and feed intakewere recorded daily. Egg quality traits were recorded every 5 wk. Leukocyte subset countsand blood lipid profile were evaluated at the end of experiment. The results showed thatinclusion of 150 g/kg RB negatively influenced (P < 0.05) egg production (EP), feed conver-sion ratio (FCR), shell weight and shell thickness. Significant reductions (P < 0.05) in theblood triglyceride and total cholesterol were observed with increasing dietary inclusionlevels of RB. Although, dietary NPP levels did not influence any of the performance traits,the low-NPP diets caused a decrease (P < 0.05) in shell weight and shell thickness whencompared with normal-NPP diets. The H/L ratio, as a stress indicator, was also increased(P < 0.05) by low-NPP diets. These adverse effects were partially overcome by the addition ofmicrobial phytase (PHY). Supplemental PHY improved (P < 0.05) EP, FCR and unmarketableeggs but the magnitude of the responses was greater in low-NPP and high-RB treatments,resulting in significant RB × NPP × PHY interactions. Egg mass, shell weight and shell thick-ness were also improved (P < 0.05) by PHY addition but the response was greater at thehighest concentration of RB, resulting in a significant RB × PHY interaction. Responses werealso greater (P < 0.05) in low-NPP diets as indic
