Protein is needed to supply essential amino acids and nitrogen to the horse. The horse uses these subunits of protein for building muscle, structural tissues, organs, hormones, and several other vital parts or substances for life. Crude protein is the amount of protein that is contained in a feed and is determined chemically by determining the amount of nitrogen in a feed and calculating the corresponding amount of protein that would be represented of the determined amount of nitrogen. Digestible protein is determined experimentally with feeding trials and is the amount of protein that is digested and enters the body from the horse’s intestine. Protein quality refers to the amounts of specific amino acids in the protein of a feed. Some feeds have larger amounts of needed amino acids; hence, they are of relatively “higher quality.” You can find more information on nutrition and nutrients in the eXtension Web site’s section on nutrients.