In Vitro and In Vivo Immunological Measurements in Growing Lambs Fed Diets Deficient, Marginal or Adequate in Zinc

Semi-purified diets, severely deficient (basal diet, 3.7 mg Zn/kg of diet), marginally deficient (basal diet + 5 mg Zn/kg of diet) or adequate (basal diet + 40 mg Zn/kg of diet) in zinc (Zn), were used to determine the effect of dietary Zn on humoral and cell-mediated immune responses in growing lambs. Dry matter intake, daily gain, serum alkaline phosphatase activity and serum Zn were lower for severely deficient lambs. The total number of peripheral blood leukocytes and an in vivo response to phytohemagglutinin were not affected by treatment. Severe Zn deficiency resulted in a lower percentage of lymphocytes and higher percentage of neutrophils in peripheral blood. Lymphocyte blastogenesis, measured by [3H]thymidine incorporation into peripheral blood lymphocytes, was lower when lymphocytes from severely deficient lambs were incubated with concentrations of phytohemagglutinin that were suboptimal for maximum proliferation. Blastogenesis was higher when lymphocytes from severely deficient lambs were incubated with a pokeweed mitogen concentration that was in excess of that needed for maximum proliferation. Immunoglobulin G titers, in response to lysozyme injection, were unaffected by dietary Zn. Severe Zn deficiency affected feed intake, weight gain, the percentages of peripheral blood leukocytes and in vitro lymphocyte blastogenesis to concentrations of mitogens that were not optimal for maximum pro-liferation. However, marginally deficient lambs were not different from Zn adequate lambs, indicating a dietary Zn level of 8.7 mg Zn/kg of diet was adequate for the parameters measured.