Reproduction and Body Weight of Mice after Long-Term Selection for Large Litter Size

Abstract

A line founded by selecting the 24 largest litters from a large Swiss randomly bred mouse population was selected for increased litter size at birth, during 29 generations. Per generation 96 females were mated to 24 males, and the 24 largest litters were selected. Litters were not standardized. Average selection differential was 3.69 young (i = 1.54). Total selection response was an increase from 8 young in the base population to 14 young born in generation 29 of the selection line. Realized heritability was .11 ± .01 (P<.01). Changes in heritability were not significant during the 29 generations. Higher litter size in the selection line was mainly caused by higher ovulation rate, while lower losses before and after implantation contributed to the difference. Correlated responses in number of mice that died between 0 to 12 days, and between 12 to 21 days of age, and in body weights at 21 and 56 days were not significant. Litter size and litter weight at 12 days and number of mice that littered of the 96 exposed per generation increased (P<.01), while number of days from exposure to male to date of littering decreased (P<.01). Copyright © 1978. American Society of Animal Science . Copyright 1978 by American Society of Animal Science.