Assessment of trace mineral status of ruminants: A review

Abstract

An assessment of the trace mineral status of ruminants begins with clear objectives. These may be to determine whether a nutrient deficiency exists, to assess the prevalence of a deficiency, or to estimate the endogenous reserves of trace minerals. The sampling size needed for assessment is a function of the herd size, expected prevalence of deficiency or toxicity, desired confidence of the assessment tool, and the estimated standard deviation of the assessment criteria. The trace mineral status of animals is best described by concentrations in liver. Correlation coefficients between concentrations of trace minerals in blood and liver are highest in deficient animals because endogenous reserves are depleted. Concentrations of Zn, Cu, and Se in plasma also are affected by infection, stress, pregnancy, and erythrocyte hemolysis. Because erythrocytes in cattle have a 160-d life span, concentrations of trace minerals in whole blood change more slowly than those in plasma in response to changes in intakes of trace minerals. Improvements in sensitivity of blood measures to assess trace mineral status await determination of the most critical metalloenzyme activity. At present, metalloenzyme activities are seldom more useful than concentrations of minerals in plasma and often are impractical because of loss of activity in shipment to the laboratory. Perhaps the ultimate assessment tool is the response of animals to supplementation.