The effects of selection at different ages for high and low body weight on the pattern of fat deposition in mice

Abstract

SUMMARYTwo pairs of lines of mice, selected for High and Low weight at 5 weeks of age (H5and L5) and at 10 weeks of age (H10and L10) over 15 generations, were compared with each other and an unselected control line (QC) at three different ages, i.e. at 5, 10 and 21 weeks of age. Differences in percentage fat between High and Low lines were small at 5 weeks, clearcut at 10 weeks and at 21 weeks the High lines were almost twice as fat as the Low ones. The H5line was slightly fatter than the H10line at all three ages and the L10line was fatter than the L5line at two ages. The developmental pattern of fat deposition was unaffected by selection for high or low weight at 5 weeks, i.e. the relationship between fat weight and carcass weight was similar in the H5, L5and QC lines. Selection at 10 weeks affected the level of fat at low carcass weights and the relative rate at which fat was subsequently deposited. The different correlated responses resulting from selection at 5 and 10 weeks are explained in terms of genetic variation in (1) the rate of food consumption, (2) the efficiency of energy utilization for growth, and (3) the relative amount of fat deposited up to the age at selection.