Influence of laying on lead accumulation in bone of mallard ducks

Paired mallard ducks (Anas platyrhynchos) were given No. 4 lead shot, and bone lead concentrations were compared in drakes and in laying and nonlaying hens. Lead accumulation was significantly greater in bones with a high medullary content (femur and sternum) compared with bones with a lower medullary content (ulna-radius or wingbones). In dosed groups, hens always contained higher bone lead residues than drakes. After dosage with one shot (approximately 200 mg lead), lead in femurs of laying hens averaged 488.4 ppm compared with 113.6 ppm in nonlaying hens. Femurs of drakes averaged 9.4 ppm lead. Dosage with the second lead shot did not result in further accumulation of bone lead in hens, but increased bone lead concentrations threefold in drakes, suggesting that saturation levels for bone lead had already been reached in the hens after ingestion of one shot. There was no demonstrable relationship between egg production and bone lead residues. The high lead residues, found in medullary bones of laying hens indicate that sex and physiological condition are major factors influencing lead absorption by bone.