The effects of different levels of dietary lead on zinc metabolism in dairy calves

The effects of feeding diets containing 500 or 1500 ppm added lead as lead sulfate on zinc and zinc-65 metabolism in Holstein bull calves were investigated. Zinc absorption was slightly (not significantly) reduced in the calves fed lead. Fecal zinc excretion was increased by the lead diets by day 24 of the experiment. Dietary lead had no significant effect on zinc in blood. Except for the tibia, muscle, and brain, stable zinc decreased in all tissues of calves fed the 1500 ppm lead diets, and differences were significant in pancreas, heart, and testicle. A significant decrease was noted in pancreatic zinc in pancreas of calves fed 500 ppm lead. Tissue zinc-65 concentrations were decreased significantly by lead in the tibia and muscle. Intestinal tissue zinc was not affected materially by lead. Dietary lead had very little effect on cellular distribution of zinc in the liver and kidney. In the mucosal cells of the small intestine, lead increased zinc-65 in the cytosol while decreasing it in the crude nuclear fraction. This effect occurred in a linear fashion in all three sections of the small intestine as dietary lead increased.