EFFECT OF SELENIUM SUPPLEMENTATION ON COPPER METABOLISM IN DAIRY COWS

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Abstract
Eight Holstein cows were fed a diet supplemented with selenium at a subtoxic level (2.37 mg kg−1 dry matter), or the same diet without selenium supplementation (0.31 mg kg−1 dry matter), for 276 d of lactation. Copper-65, a stable isotope, was administered intravenously after 14 d of adaptation to the diets, and samples of milk, blood and liver were obtained at intervals throughout the trial. The effect of selenium supplementation on copper metabolism of the cows was evaluated by determining concentrations of copper in plasma, milk and liver, by determining the activities of ferroxidase in plasma and superoxide dismutase in erythrocytes and by determining the pattern of dilution of the copper-65 tracer in plasma, milk and liver. No effect of selenium supplementation on any of the parameters of copper metabolism was observed. It was concluded that an interaction between copper and selenium did not occur under the conditions imposed in this study. Key words: Copper, selenium, interaction, dairy cows, copper stable isotope