The Basal Metabolism of Mature Chickens and the Net-energy Value of Corn^

One of the great contributions of Armsby to the science of animal nutrition was the demonstration that the requirements of animals for nutrients, and the values of feeds in covering these requirements, are two separate and distinct problems, requiring different experimental methods for their solution. The requirement of an animal for energy, for example, must involve a study of the heat production of the animal and of the energy content of animal tissues and secretions produced during growth, fattening, egg production, gestation, and lactation. The energy requirements are, therefore, best expressed in terms referring to the animal rather than to the feed; hence the measurement of animal requirements in terms of feed or digestible nutrients is an incomplete and an inaccurate measurement, however valuable it may be in practical animal husbandry. According to Armsby (1)^^ the measurement of the true value of feeds as sources of energy to animals involves a determination of the energy content of the feed and of all losses of energy incurred in its utilization by the animal. If the latter are subtracted from the former, the ''net-energy^' value of the feed is obtained. A more complete definition of the actual energy value of a feed to the animal has never been proposed, nor one of greater sigmficance as a guide to experimental investigation. It would seem that the same conception might be applied to other nutrients.