Lush, immature pastures, especially cool-season grasses and wheat pasture, are magnesium deficient or have forage conditions that cause a magnesium “tie-up,” resulting in a health condition referred to as grass tetany. If this is a problem in your area, you should use extra magnesium in the form of magnesium oxide and add this to the mineral mix at the rate of 15 to 20 percent of the total mineral formulation. To prevent grass tetany, cows typically need from 50 to 60 grams of magnesium oxide per day. When magnesium is added to a typical mix, it may be less palatable, and it may be necessary to add 6 to 10 percent of a flavoring agent such as molasses or soybean meal to ensure desired animal intake.

Commercial mineral supplements are also available that contain 8 to 10 percent magnesium for cows and 4 to 6 percent for stockers.