Zinc, Copper, Manganese, and Selenium in Dairy Cattle Rations

The trace minerals zinc, copper, manganese, and selenium are components of a wide variety of enzymes and proteins that support metabolism, growth, production, and reproduction. Trace mineral supplements are added to dairy cattle rations to prevent mineral deficiencies, and supplementation has traditionally been provided in the form of inorganic salts. When these inorganic salts dissociate in the reticulo-rumen, omasum, and abomasum, the trace minerals can form indigestible compounds with other feed components which renders them unavailable for absorption in the intestines. Organic trace mineral supplements that are both stable in the digestive tract and available for intestinal absorption have the potential to be more available to the cow than inorganic supplements. However, measurement of bioavailability of trace mineral supplements is difficult, and studies comparing organic to inorganic trace mineral supplements do not consistently show increased bioavailability. Organic trace mineral supplementation has been shown to increase animal production response relative to inorganic trace minerals in some studies, with or without a concurrent increase in measures of bioavailability. Some studies have shown that trace mineral supplementation above predicted requirements improves animal health, likely due to the antioxidant functions of Zn, Cu, Mn, and Se. Supplementation of trace minerals during times of oxidative stress may enhance disease resistance.