GROWTH EFFICIENCY IN MICE SELECTED FOR INCREASED BODY WEIGHT

Abstract

To elucidate the effect of selection for increased growth upon growth efficiency (gain:feed), growth and feed consumption patterns were studied in three lines of mice. Two of the mouse lines (H lines) had been selected for high 42-d body weight while the third was an unselected foundation (FP) population. The two H lines differed in population size and were designated as the high-large (HL) and high-small (HS) lines. Logistic growth curve analysis revealed that, in terms of growth rate and mature body size, the three lines could be ranked as HL > HS > FP. When considered relative to age, the feed consumption of the H line mice exceeded that of FP mice. When growth efficiency was considered relative to body weight, HL mice exhibited a significantly higher efficiency than either HS or FP mice. However, when considered relative to degree of maturity (body weight/asymptotic body weight), differences in growth efficiency were greatly reduced. This effect of maturity upon growth efficiency is compatible with the previous suggestion (Taylor and Murray 1987) that many growth-related variables are strongly associated with an animal's "target" mature body weight. A corollary of this suggestion is that much of the well characterized selection responses, of "high-growth" selection lines, may be accounted for by genetic differences in a factor associated with the elevation of their target mature body weight. Key words: Growth-selected mice, growth efficiency, mature body weight