PREWEANING WEIGHT AS A MEASURE OF MILK PRODUCTION IN MICE

Abstract

A cross-fostering experiment with random-bred mice was performed to determine the importance of milk production in 12-day weight of a litter containing either six or eight young and in litter weight gains (litter weight gain from birth to 12 days, and litter weight gain from 1-hour nursing at 12 days). Three and four dams that produced young on the same day formed a cross-fostering set in the six-young and eight-young groups, respectively.In the six-young and eight-young groups, milk production accounted for 65 and 66% of the variance, respectively, in 12-day litter weight. Litter weight gain from birth to 12 days and litter weight gain from 1-hour nursing at 12 days had 74 and 61% of their variance accountable to milk production in both young groups. The findings indicate that the importance of milk production (phenotype) in 12-day litter weight and litter weight gains is virtually the same in the two groups. The conclusion was drawn that unless the values of genetic parameters involved are different for litters of six and eight young, the accuracy of estimating the additive genotype of milk production from 12-day litter weight or litter weight gains is similar when a mother suckles six to eight young.