Effect of varying dietary Zn levels on Zn-intake (A), Zn-excretion (B) and Zn-retention (C) in broilers. Zn-40, Zn-50, Zn-60, Zn-70 conatined 40, 50, 60 and 70 ppm Zn per kg diets, respectively. Significant difference between the treatment mean values are represented by superscript on the bars (P<0.05).