PHENOTYPIC VARIATION IN RESIDUAL FOOD-INTAKE OF MICE AT DIFFERENT AGES AND ITS RELATIONSHIP WITH EFFICIENCY OF GROWTH, MAINTENANCE AND BODY-COMPOSITION

Food intake and body weight of 119 mice was measured from 3 to 18 week s of age. Residual food intake was calculated for each week as the var iation in food intake independent of variation in weight gain, weight maintained and sex. Growth efficiency and maintenance requirement were calculated by fitting curves to data from 3 to 18 weeks. The repeatab ility of residual food intake was low in young mice, but increased as they matured. Growth efficiency was correlated with residual food inta ke in very young mice. Residual food intake was not correlated with ma intenance requirement in young mice, but as mice matured the correlati on of residual food intake with maintenance requirement increased to 0 .6. Body composition at maturity was correlated with residual food int ake and maintenance requirement of mature mice, but a large proportion of the variation in residual food intake and maintenance requirement was independent of body composition. The results suggest that the age at which residual food intake is measured is important if it is to be used as a criterion for selection for efficiency.