Direct and correlated selection response for litter size and litter weight at birth in the first parity in mice

Two lines of mice derived from the same base population were selected for seven generations. Line S was selected to increase litter size at birth and line W was selected to increase litter weight at birth. Two replicates were made in each line. Both traits were measured at first parity and litters were not standardized. Direct and correlated response were evaluated for both traits. Expected selection response and genetic gain were evaluated at the first and seventh generation of selection. No significant differences were found between expected selection responses and estimated genetic gain. The genetic gain estimated was significantly higher (p < 0.01) for line W than line S for both traits.