Supplement 40 ppm zinc, 10 ppm copper, and 40 ppm manganese as inorganic sulfate forms. We would not add iron as our feeds and water typically contain sufficient iron (if you need a target value, 50 ppm). We recommend copper sulfate and not copper oxide because of the low availability of copper oxide. Sulfur should be at least about 10 times the nitrogen concentration, but keep total dietary sulfur below 0.4% on a dry matter basis.
Mike Hutjens, Extension Dairy Specialist, University of Illinois - Illini DairyNET
