Selection for Increased Preweaning and Postweaning Weight Gain in Mice

Abstract

Fourteen generations of selection in mice were conducted within three lines selected for increased 21-day weight (WWL), three lines selected for increased average daily weight gain from 21 to 42 days of age (ADGL) and two unselected control lines (CL). The eight lines were initiated from a base population synthesized from a four-way cross among one non-inbred and three highly inbred strains of albino mice. Generally, each line consisted of 20 litters per generation. General response patterns were similar for the three replicate lines within each selection regime (WWL and ADGL). After 14 generations of selection, the total changes in growth performance in the WWL were 2.51 g (31.4%), .112 g/day (16.8%) and 4.67 g (19.1%) for 21-day weight, 21 to 42-day average daily gain and 56-day weight, respectively. The selection responses in the ADGL were 1.67 g (20.9%), .348 g/day (52.3%) and 11.31 g (46.2%) for those same three traits. Regression of selection responses on cumulative selection differentials provided realized heritability estimates for 21-day weight of .156, .195 and .163 (average .171±.01) from the WWL and for 21-to 42-day average daily gain of .301, .273 and .248 (average .274±.015) from the ADGL. The genetic correlation between preweaning and postweaning growth rate estimated from direct and correlated selection responses was .47. The WWL and ADGL had significantly larger average litter sizes and heavier 12-day litter weights than the CL. The percentage of females exposed for breeding that produced litters was significantly reduced in the ADGL. Copyright © 1975. American Society of Animal Science. Copyright 1975 by American Society of Animal Science.