Mineral Feed Supplement for Horses. This feed contains added selenium at 2mg/kg. Guaranteed Analysis: Salt (NaCI) act 51.6% Sodium (Na) act 20.2% Potassium (K) act 8.0% Calcium (Ca) act 6.6% Sulfur (S) act 3.9% Cobalt (Co) act 23 mg/kg Copper (Cu) act 120 mg/kg Magnesium (Mg) act 1.6% Iron (Fe) act 730 mg/kg