Zinc Metabolic Adaptations in Calves Fed a High but Nontoxic Zinc Level for Varying Time Periods

Abstract

Zinc and 65Zn metabolism was studied in 12 Holstein bull calves fed a practical-type basal diet (34 ppm zinc) or the basal diet supplemented with 600 ppm zinc for 7, 14 or 21 days before sacrifice. A single tracer oral 65Zn dose was given to each animal 7 days prior to sacrifice. Supplemental zinc for 7 days caused large increases in pancreas, liver and kidney zinc followed by further substantial linear increases with time. Lesser effects were observed in small intestinal tissues. In contrast, blood zinc levels were greatly increased by feeding 600 ppm supplemental zinc for 7 days with no significant increase thereafter. Supplemental zinc decreased 65Zn absorption (P< .05) as measured by fecal excretion, with length of time fed the high zinc diet having little effect except on daily rates. Compared to controls pancreas 65Zn increased slightly with 7 days added zinc, doubled by 14 days and quadrupled at 21 days. Liver 65Zn decreased sharply (P< .05) at 7 days but increased by 21 days to near control values. These data indicate that part of the huge increases in zinc deposition accompanying breakdown of zinc homeostasis in certain tissues occurs very quickly with another portion requiring much longer. The variable time effects indicate different relative importance of the components among tissues.