An AU (animal unit) defines forage intake on the basis of a standard animal. An AU is defined as a 1000-pound cow with above-average milk ability nursing a calf that is less than three to four months of age. An AUM (animal unit month) is the amount of forage to sustain an AU for a month. For each 100 pounds over 1000, the AU increases by 0.1; therefore, a 1200-pound cow that is nursing a calf that is less than four months of age would be 1.2 AU. A calf that is over four months of age is 0.3 AU. So at this point, this pair would be 1.5 AU.
A non-lactating 1000-pound cow is considered 0.9 AU, and therefore a 1200-pound non-lactating cow would be 1.1 AU, and so on.
