Composition of growth in mice with a major gene for rapid postweaning gain.

Previous research from this laboratory identified the existence of a major gene for rapid growth in mice. This trait is expressed as rapid postweaning growth and is inherited as a single recessive gene, designated hg. The hg/hg males and females had greater (P less than .05) body weights at 49-d of age as compared with their Hg/-counterparts; 45.6 +/- .64 and 34.0 +/- .64 vs 33.2 +/- .23 and 27.3 +/- .15 g, respectively. Twenty-four male littermate pairs (hg/hg and Hg/-) were euthanized at 49 d of age for determination of carcass composition. Percentage body water was not affected by genotype (hg/hg, 66.7 +/- .5; Hg/-, 67.8 +/- .3). However, there was a decrease (P less than .05) in percentage body protein (20.2 +/- .1 vs 20.8 +/- .1) and body ash (3.4 +/- .01 vs 3.7 +/- .01) in hg/hg males as compared with Hg/- males, while percentage lipid was significantly increased in hg/hg males (8.7 +/- .5 vs 6.7 +/- .3). When carcass weights were adjusted for differences in dry weight, only body protein was significantly affected by genotype, being greater for hg/hg males (8.54 +/- .19 vs 7.70 +/- .19 g). All other components of body composition were not affected by genotype. The regression coefficient for the covariate of dry weight was significantly different from zero for all carcass components. However, there was no significant difference in the regression coefficient between Hg/- and hg/hg males for each component.(ABSTRACT TRUNCATED AT 250 WORDS)