ZINC-OXIDE AND AMINO-ACIDS AS SOURCES OF DIETARY ZINC FOR CALVES - EFFECTS ON UPTAKE AND IMMUNITY

Calf starter diets were formulated to contain 60 ppm of Zn, 150 or 300 ppm of Zn in the form of Zn-Met and Zn-Lys, or 300 ppm of Zn in the f orm of ZnO to compare relative bioavailability and effects on immunity . Holstein heifer calves were weaned at wk 5 and fed experimental star ter diets from wk 6 to 12. Feed intake, body weight, Zn concentrations in liver and serum fractions, and mineral concentrations in serum wer e measured to determine the effects of treatment. In addition, periphe ral blood lymphocyte blastogenesis, interleukin-2 production, cytotoxi c activity, and the ability of blood neutrophils to phagocytose and ki ll bacteria were assessed at wk 0, 2, 4, and 6 of the trial. Feed inta kes and body weight gains were similar among calves. Concentrations of Zn in serum were elevated in calves fed 300 ppm of Zn as Zn-Met and Z n-Lys but not in calves fed ZnO. Concentrations of Zn in liver were si gnificantly elevated by 300 ppm of Zn in the form of Zn-Met and Zn-Lys (360 mu g/g) but not by the other Zn treatments or by the control (24 5 mu g/g). No treatment had an effect on the concentrations of Lys and Met in serum; however, concentrations of Lys did decrease in serum as the age of the calves increased. There was no significant treatment e ffect on mitogen-induced lymphocyte blastogenesis, interleukin-2 produ ction, lymphocyte cytotoxicity, or phagocytic and intracellular killin g ability of blood neutrophils. These data indicated greater absorptio n and retention of Zn when administered in the form of Zn-Met and Zn-L ys than that when ZnO was administered to young calves. However, there was no advantage to the immune function of extra dietary Zn.