Toxic effects of high concentrations of zinc oxide in the diet of the chick and laying hen

1. The effects of high dietary concentrations of zinc oxide on chicks and hens were studied in four experiments.

2. Chicks given 2 000, 4 000 or 6 000 mg zinc/kg diet from 2 to 6 weeks of age grew poorly, many showing gizzard erosion and lesions of the exo‐crine pancreas. Dissecting aneurysms occurred in a few birds receiving 6 000 mg zinc/kg.

3. Pancreatic lesions were found in chicks maintained on 1 000, 2 000 or 4 000 mg zinc/kg from 0 to 4 weeks and the two higher concentrations reduced body weight and increased the incidence of gizzard erosion.

4. Histologically, gizzard lesions varied from excessive desquamation of epithelial cells, heterophils and erythrocytes into an abnormally spongi‐form koilin, to erosion of koilin, glands and pits. Pancreatic lesions could be detected only microscopically and consisted of dilation of the acinar lumina, cytoplasmic vacuolation, cytoplasmic globule formation and necrosis of the exocrine cells with interparenchymal fibrosis.

5. Similar lesions of the gizzard and pancreas were found in hens after they had received 10 000 or 20 000 mg zinc/kg diet for only 4 d.

6. Hens given 10 000 mg zinc/kg for 4 d followed by a normal zinc intake for 28 d had normal gizzards and pancreata.