Animal feed is food given to domestic animals, especially livestock, in the course of animal husbandry. There are two basic types: fodder and forage. Used alone, the word feed more often refers to fodder.

Rather than munching on grass or insects, the vast majority of animals on factory farms eat some type of animal feed—a cost-effective mixture of grains, proteins, and antibiotics designed to make them grow as quickly as possible.

Animal feeds are classified as follows: (1) concentrates, high in energy value, including fat, cereal grains and their by-products (barley, corn, oats, rye, wheat), high-protein oil meals or cakes (soybean, canola, cottonseed, peanut [groundnut]), and by-products from processing of sugar beets, sugarcane, animals, and fish, and (2) roughages, including pasture grasses, hays, silage, root crops, straw, and stover (cornstalks).