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TRACE MINERALS CONCENTRATIONS CALCULATIONS
Larry L. Berger, Ph.D.
University of Illinois
Recently I received a phone call from a sheep producer who had lost three ewes to copper toxcity. The first question asked was, “what is the upper safe limit of copper to feed to sheep?” When
I explained that many factors affected the upper safety limit, but
I would not recommend over 10 parts per million (ppm) in the diet, the caller became quite irritated. This person had hired a lawyer and had submitted samples to a lab for copper analysis. When they found the salt-trace mineral mix contained 200 ppm of copper, they were convinced this was a case of gross negligence. I then explained that I did not think the salt-trace mineral mix was the source of their problem. The caller then exclaimed, “how can you say that when you recommend less than 10 ppm of copper and the product they sell for sheep contains 200 ppm of copper, 20-fold greater than the upper recommended level?” I then tried to explain that the salt- trace mineral mix is only a small part of the diet, usually 1% or less and at 1% of the diet it would only contribute 2 ppm of copper in the total diet. Over the phone the caller was unconvinced and wanted to see the calculations in writing.
The purpose of this paper is to review the calculations involved in determining trace mineral concentrations and to give some general guidelines in estimating the contribution from each source in the diet.