Effect of High Dietary Zinc upon Zinc Metabolism and Intracellular Distribution in Cows and Calves

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Abstract
Changes in the Zn metabolism were investigated in mature nonlactating Holstein cows and 4 mo. old calves fed high but nontoxic amounts of dietary Zn. Increasing dietary Zn of calves from 42-642 ppm elevated the Zn content of liver and pancreas 600% and 1400%, respectively. The elevated Zn in liver and pancreas involved a substantial increase in all intracellular fractions, with the largest amount associated with a 10,000 MW protein in the soluble cell fraction. This Zn-binding protein may protect the cell against damage from increased Zn. A comparable increase in dietary Zn of mature cows did not affect Zn content of liver or kidney nor alter the intracellular distribution of Zn in the liver. In mature cows, homeostatic control mechanisms which regulate the Zn content of tissue are much more effective than in calves. Mature cows probably are able to tolerate higher concentrations of dietary Zn.