Invited Review: Assessing trace mineral status in ruminants, and factors that affect measurements of trace mineral status

The purpose of this article is to review criteria for assessing copper, zinc, manganese, and selenium status in ruminants. Factors that affect measurements of trace mineral status also will be discussed. Published scientific literature was the primary source of information reviewed. When assessing mineral status, it is always good to analyze the diet or forages being consumed for the mineral of interest as well as other minerals that may affect its requirement. Liver is the best indicator of both low and excess Cu status. Plasma Cu concentrations do not decrease below normal values until liver Cu stores are mostly depleted, but a plasma Cu concentration less than 0.4 mg/L suggests Cu deficiency. Severe Zn deficiency can be diagnosed based on extremely low plasma or serum Zn concentrations (less than 0.5 mg/L) or on clinical signs of Zn deficiency that respond to Zn supplementation. It is important to note that infections or acute stress may cause plasma Zn concentrations to temporarily decrease to levels consistent with Zn deficiency. There is currently no reliable indicator of marginal Zn deficiency. Several criteria have been measured in an attempt to assess Mn status. However, no criteria have been demonstrated to accurately predict Mn deprivation. Whole blood or liver Se concentrations are useful in assessing Se status. When interpreting whole blood or liver Se concentrations, it is important to consider whether dietary Se is being derived from organic or inorganic sources. The most appropriate measurement criteria to assess trace mineral status in ruminants depend on the trace mineral being considered. Liver copper is generally a good measure of low as well as excess Cu status. Liver or whole blood Se concentrations are reliable measures of Se status if one takes into account the source of dietary Se. Unless clinical deficiency signs are apparent, it is more difficult to assess Zn and Mn status. In the absence of disease or stress, plasma or serum Zn concentrations below 0.5 mg/L suggest possible severe deficiency. No reliable predictor of marginal Zn deficiency has been determined. Currently, no reliable indicator of Mn status has been identified.