Serial composition during growth in mice with a major gene for rapid postweaning growth

The chemical composition of growth in mice having a major gene for rapid post-weaning growth (hg/hg) was compared to that of their normal counterparts (Hg/-) at repeated intervals from 21 to 57 days of age. Male mice of both genotypes were sacrificed at 3 day intervals from 21 to 42 days of age and at 5 day intervals thereafter to day 57 of age for determination of body composition. By day 57 the hg/hg mice weighed 44.2 g while the Hg/- mice weighed 31.9 g. Analysis of changes in body water, protein, fat and ash across ages demonstrated that the hg/hg mice had significantly greater percents of body water and fat while having less protein and ash as compared to the Hg/- mice. When the effect of body weight was removed by covariance analysis, the difference in body lipid between genotypes was no longer significant. The hg/hg mice continued to maintain a slightly but significantly greater amount of water in the body while protein and ash levels remained lower than in Hg/- mice. Age also significantly influenced the amount of water, protein and ash in both mouse genotypes. It was concluded that the very slight, but significant differences in amount of water, protein and ash in the hg/hg mice were the result of a slower rate of maturing. The gene (hg) seems to have a general influence on all chemical components of growth and apparently does not alter any specific chemical component of growth.