Animal feed is food given to domestic animals in the course of animal husbandry. There are two basic types: fodder and forage. Used alone, the word feed more often refers to fodder.
Cows and sheep need 8 kg of grain for every 1 kg of meat they produce, pigs about 4 kg. The most efficient poultry units need a mere 1.6 kg of feed to produce 1 kg of chicken. Farmed fish can also be fed on grain and use even less than poultry.
The two most important feed grains are maize and soybean, and the United States is by far the largest exporter of both, averaging about half of the global maize trade and 40% of the global soya trade in the years leading up the 2012 drought. Other feed grains include wheat, oats, barley, and rice, among many others.
Traditional sources of animal feed include household food scraps and the by-products of food processing industries such as milling and brewing. Material remaining from milling oil crops like peanuts, soy, and corn are important sources of fodder. Scraps fed to pigs are called slop, and those fed to chicken are called chicken scratch. Brewer's spent grain is a by product of beer making that is widely used as animal feed.
Premixes are composed of micro ingredients such as vitamins, minerals, chemical preservatives, antibiotics, fermentation products, and other ingredients that are purchased from premix companies, usually in sacked form, for blending into commercial rations.
Because of the availability of these products, farmers who uses their own grain can formulate their own rations and be assured that their animals are getting the recommended levels of minerals and vitamins, although they are still subject to the Veterinary Feed Directive.
According to the American Feed Industry Association, as much as $20 billion worth of feed ingredients are purchased each year. These products range from grain mixes to orange rinds and beet pulps.
In agriculture today, the nutritional needs of farm animals are well understood and may be satisfied through natural forage and fodder alone, or augmented by direct supplementation of nutrients in concentrated, controlled form. The nutritional quality of feed is influenced not only by the nutrient content, but also by many other factors such as feed presentation, hygiene, digestibility, and effect on intestinal health.