In areas of intensive animal production heavy metals such as zinc (Zn), which is present at high concentrations in poultry excreta in relation to plant requirements, may be at the origin of soil phytotoxicity This study was conducted in order to determine the effect of decreasing dietary Zn content on growth, plasma, tibia and whole body Zn concentrations, immune function, enzyme activity, Zn body retention and Zn concentration in excreta in broilers. 2. Two experiments were carried out using 160 and 80 1-day-old chicks. Broilers received diets with increased Zn contents of 20 to 190 mg/kg. In experiment 1, two sources of zinc methionine were compared to zinc sulphate. 3. A dietary Zn concentration of 45 mg/kg was sufficient to obtain normal broiler performance at 21 d of age. 4. Tibia and plasma Zn concentrations increased linearly with Zn dietary content and reached a plateau at 75 mg/kg, whereas the whole body Zn was saturated when the dietary Zn content was 90 mg/kg. 5. Antibody titres in response to SRBC injection and plasma alkaline phosphatase activity were not affected by dietary zinc concentration. 6. When the dietary Zn content was decreased from 190 to 65 mg/kg, body Zn retention was increased from 8% to 20% and Zn concentration in broiler manure was reduced by 75%. 7. Zn sources had no effect on the parameters measured in this study. 8. A nutritional approach, that is by lowering dietary Zn supplementation may reduce the risks of phytotoxicity in the soil resulting from excessive Zn concentration in manure.
