Selection for different growth parameters in laboratory mice and its correlated effects on body composition and organ weights.

Body composition and organ weights were determined in male mice sampled from 4 different lines of a selection experiment: DU-6P (selected for high protein amount), DU-6 (selected for high body weight), DU-6 + LB (selected for an index combining body weight and endurance fitness) and DU-K (unselected control line). Selection was carried out under the conditions of ad libitum feeding and standardization of litter size at birth. In all 3 selection lines a significant direct selection response was shown. While fat in lines DU-6P and DU-6 + LB remained normal, it increased after selection for body weight (DU-6) significantly. Up to generation 13 the average increase of fat was 0.32% per generation. Investigations on 28 to 80 days old mice showed, that males of this line were fatter before, at and after the age of selection (42 days). After 9 generations the body weight of selected mice was significantly increased by 23 to 29%. The absolute organ weights of hearts, livers and kidneys were also significantly higher, while the relative weights of hearts and kidneys decreased. The relative liver weights were in the selected lines higher, but only the difference DU-6 vs. DU-K was significant.