Magnesium oxide is a source of magnesium (54 percent by weight) and functions as an alkalinizer. It can increase uptake of milk fat precursors by the mammary gland. Solubility and particle size can affect rumen action. Magnesium has always been essential in animal diets for normal appetite, growth and reproduction. Since forages and grains are often deficient in Magnesium, a supplemental source with high biological availability is important to assure top animal performance.