Grass tetany, caused by a dietary deficiency in magnesium, typically occurs in cattle during spring, when lush, rapidly growing forage provides an inadequate level of the mineral. Left untreated, grass tetany can be fatal to cattle. University of Nebraska Animal Scientist Rick Rasby, PhD, says inadequate dietary sodium also plays a role, as does excess potassium. Sodium helps transport magnesium into cells, he says, and excess potassium consumption interferes with magnesium absorption from the gut, exacerbating the condition of low dietary magnesium. Magnesium oxide is the typical supplement for preventing grass tetany, he says. Its bitter flavor can discourage cattle from consuming adequate levels, but feed companies have worked to produce more palatable supplements containing magnesium oxide. Spring supplementation with magnesium is critical in areas where grass tetany has occurred. Rasby also recommends supplementing salt to provide adequate sodium, and taking care not to supplement excessive potassium.