Grass tetany is a condition in cows due to low magnesium levels in the blood which can lead to death. Grass tetany is more likely in lactating cows grazing cool-season annual forages, especially older cows or cows nursing young calves. Mineral supplements designed to provide additional magnesium should be considered to help prevent grass tetany in cows grazing cool-season annual forages. Minerals supplements with a target intake of 4 ounces per day should contain at least 5% magnesium. Monitor mineral intake as higher levels of magnesium often reduce mineral intake and good intake of the mineral supplement is critical.