Journal of Animal Science, Vol 75, Issue 8 2016-2023, Copyright © 1997 by American Society of Animal Science

JOURNAL ARTICLE

The effect of adding further traits in index selection

B. Sivanadian and C. Smith
Department of Animal and Poultry Science, University of Guelph, Ontario, Canada.

The effect on genetic and economic response of adding further traits in index selection was studied. This was done first using the true parameters and then using simulated parameter estimates and with "bending" to ensure consistent matrixes. The extra responses obtained in the full aggregate genotype were expressed as a percentage of the response before adding the trait. For simplicity the cases studied were limited to 2 to 4 traits, and to a range of simple parameter sets. The extra response from adding a further trait in index selection was very variable, but was often very large. As a simple rule, adding a trait with a high relative product (ah2) of the standardized economic weight (a) and heritability (h2) gave large extra response. Adding a trait with lower ah2 value gave less extra response. The extra responses were smaller if the correlations between the added trait and other traits with high relative ah2 were favorable and were larger if the correlations were unfavorable. With estimated parameters, the results from adding a further trait in index selection were more variable. For many cases the increase in the response was still large but for some cases the response was reduced. With poor parameter estimates the number of traits in index selection should be limited to those with the larger values of ah2. As the parameter estimates improve, more traits can be added without reducing overall genetic response. Even though some general tendencies have been discerned, there was much variation in the extra responses obtained.