Effects of dietary zinc upon tissue zinc and percent unsaturated plasma-zinc binding capacity.

Calves were fed 520 ppm zinc for 21 days, then placed on a low zinc diet (20 ppm zinc) for 35 days to determine the biological availability of zinc reserves of tissue. Concentrations of zinc in liver and kidney were elevated greatly by feeding high dietary zinc for 21 days and continued to increase with time. On the low zinc diet, the tissue burden of zinc decreased within 35 days to those comparable to calves initially fed low zinc. Likewise, both zinc in plasma and percent capacity of unsaturated plasma for binding zinc were near negative controls 21 days after removal of calves from high zinc diets. Tissue stores of zinc will not maintain adequate zinc in blood for extended periods, and hence, they probably will not sustain optimal feed intakes and growth rates of calves on low-intakes of zinc.