Genetic Parameters in Progeny-Test Selection for Field Performance of Strain-Cross Layers

Abstract

Heritabilities, genetic and phenotypic correlations and sire × location interaction were estimated for 14 traits from hierarchial covariance analysis within each of four 5-week hatching periods in 9 years. Numbers averaged 93 sires, each with 61 pullets from 11 or 12 dams of two lines distributed among 5 to 14 single-cage field locations, in each of 36 period-years and totalled 204,235 pullets from 3,354 sires. Inbreedings increased .4 to .7% per year but was uncorrelated with reproductive rate or selection applied. Heritability estimates were very stable over time and between seasons, with empirical SE for means of .4 to 1.6%. Lower heritabilities across than within locations, justify multiple-location progeny tests, especially for egg production, sexual maturity, flightiness, shell defects and blood spots.Genetic correlation (rG) changed with time only for body weight with production rate (.03 ± .01 per year) and between seasons only for production rate with egg size and shape, with empirical SE of means for rG of .02 to .04. Important antagonistic genetic correlations were those of egg production and sexual maturity with egg size and specific gravity (−.2 to −.4 ) and of body size with egg size (.4). Corresponding phenotypic correlations were made less antagonistic by favorable environmental correlation. Dam component correlations were made less antagonistic than sire correlations by more favorable correlations for dominance and maternal effects. Favorable genetic correlations increased expected gains from 12-trait index selection less than the unfavorable correlations reduced it. Predicted response in 12-trait breeding value from sire selection was 96% of maximum when only adult mortality, % production, egg size, body size and sexual maturity of progeny were used; addition of excitability and six egg quality items should improve all except specific gravity but reduce progress in egg size.