Effect of Calorie Intake on Nitrogen Retention in the Immature Fowl.

Munro (1951) showed that nitrogen retention in rats is reduced when calorie intake is restricted. Although an adaptive process to continued moderate calorie restriction was demonstrated with dogs (Rosenthal & Allison, 1 9 5 1 ) and man (Drury, Vaughan & Hannon, 1959), a linear relationship between N balance and the amount of carbohydrate given along with the protein of the diet was observed in rats (Thomson & Munro, 1955). The sparing effect of dietary fat on N has been demonstrated with rats by Cohn & Joseph (1956) and Schreiber & Elvehjem (1955), with dogs by Ontko, Wuthier & Phillips (1957) and with man by Swift et al. (1959) . Rand, Scott & Kummerow (1958) substituted maize oil isocalorically for glucose and reported improvement in growth and protein retention as measured by carcass analysis of representative chicks. In our laboratories we are interested in the effect of calorie intake of other than nitrogenous origin on N retention in the fowl. Earlier studies on the effect of diet on Newcastle-disease virus (NDV) infection in chicks (Squibb, 1961) showed that nutrient intake was significantly lower during the active involvement stage of the disease. Sanslone & Squibb (1962 b ) later demonstrated that N balance was severely depressed during the course of NDV infection. The extent to which NDV influenced the depression was related to the virulence of the infection, which in turn affected dietary N intake. In the trials reported here, N retention was measured in chicks given a wide range of calorie intake, wherein calories of protein origin were held constant but those from other than protein sources were varied.