Genetic variation in litter size and 12-day weight in mice and their relationships with post-weaning growth

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Abstract
SUMMARY: Data from a random-bred population of mice were used to examine the sources of variation in litter size and 12-day body weight, and, the genetic relationships between these traits and post-weaning body weights and body-weight gain from 3 to 6 weeks of age (post-weaning gain). The genetic model included maternal genetic effects in addition to the usual direct (individual) genetic effects. Such maternal genetic effects may be important to an understanding of traits like 12-day body weight of mice, where the young depend to a large extent on the mother for early postnatal nutrition.Analysis of litter size yielded a paternal half-sib heritability estimate of 0·34±0·19, while twice the daughter-dam regression was 0·23 ± 0·08. The repeatability of litter size was 0·51±0·07. The correlation between direct genetic effects on litter size and those on 3-, 6-, and 8- week body weights and post-weaning gain were –0·18,0·36,0-34 and 0·58 respectively. The correlation between direct genetic effects on litter size and 12-day weight was positive (0·41), while the genetic correlation between maternal effects on 12-day weight and direct effects on litter size was negative (–0·37).Analysis of 12-day weight showed that direct and maternal genetic effects were important sources of variation, but there was a large negative correlation (-0·88) between these effects. The usual genetic correlations between 12-day weight and post-weaning body weights were positive while post-weaning gain yielded a negative estimate. However, there appears to be a general negative correlation between direct genetic and maternal genetic effects in this population, for all such correlations were negative except that between direct effects on 12-day weight and maternal effects on post-weaning gain.