Low fibre and high energy feeds are classified as "concentrates". Concentrates are feeds that are high in energy and low in fibre, with a low content of crude fiber, and include grains and oilseeds. They are used to supplement the diets of animals and are typically given in smaller amounts than roughages or basal feeds, which are high in fibre and low in energy. The main function of concentrates is to supply energy and protein to meet the animal's nutritional requirements. They can be used to supplement grazing or forage diets, or as the main source of nutrition in confinement feeding systems.