(AU) a measure of livestock concentration on a range; considered to be one mature cow of approximately 1,000 lb (436.6 kg), either dry or with a calf of six months of age or less, consuming about 26 lb (11.8 kg) of forage on an oven-dry basis —note animal unit may be used to describe other kinds and classes of grazing animals expressed as an equivalent —see animal month, animal-unit conversion factor, animal-unit equivalent, animal-unit month This definition last updated 10/23/2008