Voluntary Caloric Intake of the Growing Rat

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Abstract
The voluntary food consumptions of 21 female and 17 male rats from 7 litters were studied during the first 12 weeks after weaning. During the second week after weaning the voluntary caloric intake per unit of surface area increases over that observed in the first week; and thereafter it decreases, leveling off at a value between 12.5 and 13 Cal. per square decimeter per day. To some extent this equilibrium value may be related to the proximate composition of the ration. Given rations of the same proximate composition but differing in their ability to promote growth as a consequence of differences in protein quality, the voluntary caloric intake per unit of surface area per day was constant during 5-week growth studies, regardless of the quality of the protein component, when the protein source was casein, beef, whole egg, peanut flour or wheat gluten. This apparent constancy of unit caloric intake emphasizes that the primary urge in the ingestion of food is the satisfaction of energy requirements and that, other things being equal, if growth ensues it is, within limits, an accident of the make-up of the ration. The data indicate that animals will be more uniform in their growth responses if they are selected on the basis of sex and weight at a given age than if the latter factor is ignored in favor of the criterion that they be litter mates.