A model was developed to expand NRC requirements for beef cows from two constant amounts of milk production to six lactation curves; it calculates monthly lactation requirements for nine mature sizes of cows. To aid in allocating forage, a system was presented for determining metabolizable energy requirements for the beef cow-calf unit. Requirements for the cow-calf unit range from equivalent to NRC during early lactation to values 70% higher than NRC estimates near the end of lactation; errors in pasture allocation can reduce weaning weight severely.