Numerical Experiments on the Effectiveness of a Two Traits Family Index Selection for a Reproductive Performance in Pigs

The accuracy of selection for reproductive performance is generally low because of their sex-limited expression and low heritability. In the present study, the correlated response caused by an adoption of another trait as a selection criterion was theoretically evaluated in a family index selection for a reproductive trait of pigs via numerical experiments. The heritability of the reproductive trait was assumed to be 0.1, while the heritability of the other trait and their genetic correlations were changed in various magnitudes during the experiment. The accuracy of the family index selection in regard to the reproductive trait generally increased with the increasing heritability of the other trait and the genetic relationship between the two traits. The increase in the accuracy of selection caused by the change in the genetic correlation (rG) from 0.05 to 0.70 under constant heritability of the other trait (h02) was larger than that caused by the change in h02 from 0.05 to 0.70 under constant rG. When the absolute value of the genetic correlation was from 0.3 to 0.4, the expected genetic gain in the reproductive trait from the two traits family index selection was as large as that from the family index selection with the reproductive trait only, and the expected genetic gain in the other trait was equal to that from individual selection for the trait. If the genetic relationship grew stronger than this, the rates of increase in the predicted genetic gains of the two traits were accelerated.