Response to long-term selection for egg production in laying hens

1. A White Leghorn line was selected for part-record hen-housed number of eggs from 1962 to 1990. Genetic changes were estimated as deviations from its unselected control line. 2. Over the first 10 generations with selection almost exclusively for number of eggs to the age of 273 d, all traits, except rate of mortality, showed significant changes. Regressions per year were: 273 d production, 3.07 eggs; 497 d production, 5.18 eggs; production from 274 to 497 d, 2.43 eggs; age at first egg, -2.33 d; mean weight of first 10 eggs, -0.82 g; body weight at 497 d, -19.02 g and rate of mortality, 0.19%. 3. Over the rest of the period increasing selection pressure for egg weight has been applied. This resulted in positive changes for this trait and no or small negative changes in egg number. 4. In general, heritabilities and genetic correlations did not change over the period of selection. The heritability of the main trait of selection, production to 273 d was 0.19 +/- 0.04 and heritabilities of egg size traits about 0.50. 5. The genetic correlation between egg production to 273 d and mean weight of first 10 eggs was estimated as -0.37 +/- 0.06 but from the observed response a realised genetic correlation of -0.97 was calculated.