Selection for increased 12-day litter weight in mice.

Area of Science:

• Animal Genetics
• Quantitative Genetics
• Animal Breeding

Background:

• Litter weight is a key indicator of early-life performance in mammals.
• Understanding the genetic architecture of litter weight is crucial for effective selective breeding programs.
• Previous studies have explored genetic parameters for growth traits in various livestock and model organisms.

Purpose of the Study:

• To investigate the effectiveness of selection for increased 12-day litter weight in mice.
• To estimate realized heritability and genetic gain for early growth.
• To partition the sources of variation influencing litter weight and examine correlated responses.

Main Methods:

• A replicated selection experiment was conducted over nine generations using mice.
• Selection was practiced for increased 12-day litter weight in standard litters of eight.
• Components of variance and genetic covariances were derived to analyze sources of variation.

Main Results:

• The pooled realized heritability for 12-day litter weight was 0.08 ± 0.04, with an observed genetic gain of 0.57 ± 0.19 g per generation.
• Direct additive genetic variance accounted for 37.0% of the total variation, while maternal effects (additive and postnatal) comprised 66.0%.
• Positive correlated responses were observed for body weights up to 56 days, but not for postweaning gain or reproductive traits.

Conclusions:

• Selective breeding can effectively increase early litter weight in mice, primarily driven by direct additive and maternal genetic effects.
• While early growth is enhanced, selection for litter weight did not negatively impact reproductive efficiency in this study.
• The findings provide insights into the genetic control of growth and maternal influences on litter performance.