Twenty Angus were individually fed 5 rations in an experiment patterned after Lucas' extra-period Latin-square change-over design using 28-day evaluation periods following 14-day adjustment periods to compare starch and sugar as important sources of energy; to raise protein level by replacing part of starch and sugar with cottonseed meal; and to raise the protein equivalent of the starch ration by adding urea. Body weight and metabolic body size had no appreciable effect on feed intake. Animals when on higher protein or protein equivalent gain faster, more efficiently, and consumed more feed than when on low protein. The ration supplemented with urea supported the fastest and most efficient gains. Consumption of rations intended to be high-energy and low-protein was very low,indicating an effect of protein level on voluntary feed intake. Ruminal protozoal distribution was normal except for animals when fed the starch ration in which the protozoan Epidinium ecaudatum was found in large numbers; animals when fed starch and cottonseed meal contained unusually high numbers of species of Diplodinium; and for low populations of the holotrich Isotricha in all rations fed.