An experiment was conducted to investigate the effect of zinc (Zn) supplementation and different concen-trations of calcium (Ca) and phosphorus (P) in wheat-based diets on the performance, immune responses and bone parameters of broiler chickens. A randomized complete block design with factorial arrangement was used (three concentrations of Zn supplementation×two concentrations of dietary Ca-P), 300 day-old broilers were assigned to six dietary treatments with five replicates of ten birds. Dietary treatments were the basal diet (control; TRT1), control plus 50 ppm Zn (TRT2), control plus 70 ppm Zn (TRT3), low Ca-P diet (0.60 to 0.30%; TRT4), low Ca-P diet plus 50 ppm Zn (TRT5) and low Ca-P diet plus 50 ppm Zn (TRT6). Ca and P in the control diet were 0.90 and 0.45% in the grower phase and 0.85 and 0.42% in the finisher phase. Changes in dietary Ca-P had no effect on body weight gain (BWG), feed intake (FI), feed conversion ratio (FCR) or serum Ca and P concentrations (P>0.05) whereas Zn supplementation increased FI (P<0.05). The addition of 50 ppm Zn increased serum P concentration (P<0.05) and dietary treatments had no effect on antibody titers against sheep red blood cells (SRBC) (P>0.05). The lowest blood heterophil (H) and the highest lymphocyte (L) percentages and lowest H:L ratio were observed in birds fed with the diet contain-ing a standard Ca-P with 70 ppm Zn supplementation (P<0.05). Dietary treatments had no effect on bone length, thickness and breaking strength (P>0.05). Tibia and fibula ash decreased by feeding lower Ca-P than the standard diet (P<0.05). It is concluded that low Ca-P diets did not have a detrimental effect on per-formance or blood and bone parameters and that Zn supplementation did not improve those parameters when feed was low in Ca-P.
