Three parameters affecting interlitter variations

We studied 3 parameters affecting average body weight differences between mouse litters and have arrived at an approximation of the contribution that each makes to such differences. These parameters are birth weight, genetically based growth potential variations, and maternal competence. We have developed methods for controlling these parameters and show that through their application we can reduce litter-average body weight differences from our normal value of more than 24% to about 3%. The vanished 21% consists of 12% due to differences in maternal competence, 6% due to growth potential differences, and 3% due to initial weight differences.