Compared with other feed grains, corn is lower in protein and slightly higher in energy . Corn contains approximately 72 percent starch on a dry-matter basis. Other important fractions in the corn kernel include protein, fiber and minerals. The protein in corn is approximately 65 percent escape or bypass protein. Escape protein is protein that is not fermented or degraded by the ruminal microorganisms, but is digested and absorbed by the animal in the small intestine. The remaining 35 percent of the protein in corn is rumen-degradable protein. Ruminal microorganisms require rumen-degradable protein for use in growth and protein synthesis. Like all cereal grains, corn is low in calcium and relatively high in phosphorus . Diets containing high levels of corn should include a supplemental calcium source, such as limestone, to prevent urinary calculi. The recommended calcium-to-phosphorus ratio in backgrounding and feedlot diets is a minimum of 2-to-1 (two parts calcium to one part phosphorus).