The purpose of this study was to investigate high concentration of dietary zinc (Zn) and to compare the effects of organic and inorganic zinc sources on hematological and biochemical parameters of blood serum in dairy cows. Eighteen dairy cows were randomly allocated to one of three dietary treatments in a randomized and blocked design. Animals in group 1 were treated as control (no zinc supplementation); whereas, animals in groups 2 and 3 supplemented with 500 mg of zinc/kg dry matter from either zinc sulfate monohydrate (ZnS) and zinc methionine (ZnM), respectively. The numbers of red blood cells, hemoglobin concentration, packed cell volume, and mean corpuscular hemoglobin concentration in the ZnM group was higher than the control group. Activities of lactate dehydrogenase and superoxide dismutase in ZnM and ZnS groups were higher (P<0.05) than the control group. There was no difference in the other metabolites between groups, but the serum zinc concentration was higher (P<0.05) in cows fed ZnM or ZnS. There was no difference among groups for biochemical parameters and some hormones in serum may due to the competition levels of zinc supplementation reducing availability of other minerals. Therefore, the results obtained may be beneficial in demonstrating the effects of zinc with no negative effects of high Zn concentration on hematological and biochemical parameters.

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