Abstract: A feed composition designed to prevent grass tetany in livestock. Neutral or acidic magnesium salts are completely dissolved in a liquid energy source to provide readily available magnesium ions which, when ingested, increase blood serum magnesium levels in the animal sufficient to avert hypomagnesemia. The liquid energy source is selected from a group of materials which are immediately absorbed from the alimentary canal without the necessity of undergoing digestion. Thus, the feed supplement provides an instantly available source of both magnesium and energy, which combination acts to prevent grass tetany in livestock.