Body Composition of Mice Selected for Rapid Growth Rate

Abstract

Chemical composition of whole carcasses of mice from three replicate lines selected for rapid growth rate and from an unselected control line was determined each generation for 10 generations. Traits studied included gain on test, feed consumed on test, liveweight at sacrifice and grams of each of the following: ether extract, moisture, crude protein and ash. Analysis of variance revealed that all main effects included in the mathematical model (generation, line, sex and age) significantly affected body composition. Within line regression analysis showed rate of gain increased significantly over generations in all lines, that the amount of all carcass components increased in the selected lines, and that ether extract increased proportionately much more in two of the lines than did the other components; in the third selected line increases in ether extract and ash were nonsignificant while proportionate changes were all nonsignificant (i.e., P<.05). The control line displayed a highly significant decrease in ether extract on both the actual and proportionate bases. A new selection regime was introduced at generation 10 and five further generations were produced, in which one line continued to be selected for rate of gain, one was selected for feed intake and one for efficiency of feed utilization. The change in selection criteria resulted in: no deterioration in rate of gain in any of the lines; no further discernable difference in body composition in the line selected for efficiency or in the control line; a progressive, fairly constant increase in all components in the line selected for gain; and a drastic increase in body size and especially in amount of ether extract in the line selected for high feed consumption. Copyright © 1968. American Society of Animal Science . Copyright 1968 by American Society of Animal Science