Trace Mineral Supplementation Is often Times Confusing

Iron (Fe), cobalt (Co), copper (Cu), manganese (Mn), zinc (Zn), iodine (I), and selenium (Se) are trace or microminerals that are commonly added to rations for dairy cattle.

Since they are needed in small amounts they are usually expressed as parts per million (PPM) or milligrams per kilogram of dry matter, which is the same. In other words 1 PPM equals 1 mg/kg.

Some common sources of these trace elements are ferrus sulfate for Fe, cobalt carbonate for Co, cuprous chloride for Cu, manganous oxide for Mn, zinc oxide for Zn, calcium iodate for I, and sodium selenite for Se.

Using these sources I calculate that less than 8 grams of total would be needed if 100% of the NRC requirements were added to a lactating cow ration. Therefore, only very small amounts are needed and are usually added with a carrier to allow proper mixing with other feed ingredients.

These sources I have used are all classified as inorganic but there are other sources besides these both inorganic and organic in nature. Inorganic sources do not have carbon atoms in the matrix and the organic sources do.

Organic sources can contain amino acids, peptides, or polysaccharides in conjunction with the metal ion. Common complexes would contain Zn, Cu, Co, or Mn. Organic sources are generally more expensive than inorganic ones and would be used selectively as a source of trace mineral.

However, there is some indication that trace minerals in organic form are absorbed and/or utilized more efficiently by animals. If absorption were the only question it would be possible to simply add more of the inorganic source to allow for a lower absorption from the gastrointestinal tract.

However, there does appear to be situations were there might be advantages of the organic form particularly in situations involving the immune system and reproductive efficiency. Also there are competing ions for absorption such as Cu, Fe, and Zn. Adding the organic source might result in absorption by a different mechanism that reduces the interference.

Some recommendations call for one fifth to one third of the total trace element supplement to be organic form depending on the element considered. Research should support the type of organic supplement that is used, however.

By Charles C. Stallings - Extension Dairy Scientist, Nutrition
Dairy Pipeline newsletter - Virginia Tech Cooperative Extension