EVALUATION OF SELECTION BASED ON SPECIFIC-GRAVITY AND EGG WEIGHT FOR IMPROVEMENT OF SHELL THICKNESS IN LAYER CHICKEN

Data collected on 4 568 pullets of 2 strains of White Leghorn were use d for prediction of shell thickness from egg weight, specific gravity and shape index. The R-2 values for prediction of shell thickness from specific gravity ranged from 65.69 to 78.01%, Inclusion of egg weight improved the prediction significant (R-2 = 69.9 to 80.0%). Shape inde x did not improve the efficiency of prediction Analysis of relative ef ficiencies of selection based on specific gravity and an index of spec ific gravity and egg weight for genetic improvement of shell thickness was made based on genetic parameter estimates. Selection on specific gravity was 7.3% less efficient than direct selection for shell thickn ess. Selection based on index of specific gravity and egg weight was o nly 1.6% less efficient than direct selection for shell thickness.