It is a common practice in the broiler industry to formulate diets to contain 100–120 mg supplemental Zn kg−1. Burrell et al. reported improved performance when broilers consumed diets formulated to contain 110mg Zn kg−1; the NRC (1994) requirement of Zn for broiler chickens is only 40 mg/kg. Excessive supplement of inorganic Zn can bring on serious environment pollution resulting from the low utilization of this element.