This volume presents portions of the results of fifteen years of cooperative research by the New Hampshire Agricultural Experiment Station and the Nutrition Laboratory of the Carnegie Institution. A large number of observations are summarized and discussed, providing a useful digest of current knowledge. Numbers of cows, steers, bulls, goats, sheep and horses were studied particularly from the point of view of energy exchange and diet utilization. The results are of practical as well as theoretical importance. One is impressed by the fragmentary knowledge of the physiology of domestic animals of economic importance, as compared with the more complete knowledge of dogs, cats, rabbits and rodents, which are the more usual laboratory animals. The need for more intensive study of the farm animals is made apparent. Fragmentary data on urine, feces, heart rate, respiratory rate and body temperature are given.