RESUMO
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.
Assuntos
Galinhas/genética , Galinhas/fisiologia , Oviposição/genética , Oviposição/fisiologia , Seleção Genética , Envelhecimento/genética , Envelhecimento/fisiologia , Animais , Peso Corporal/fisiologia , Feminino , Análise de Regressão , Fatores de TempoRESUMO
1. In a closed White Leghorn flock over a 6-year period the average increase in egg weight from the start of lay to 37 weeks of age was 12.6 g. 2. The heritability of this egg weight increase was estimated at 0.36 +/- 0.06. 3. The genetic correlations of egg weight increase with other characteristics were: age at first egg -0.50, early egg weight -0.51, 37 week egg weight 0.42 and egg production to 273 d 0.44. 4. It is predicted that with unit selection intensity the direct response in egg weight increase will be -1.30 g, with correlated responses in age at first egg of 2.1 d, early egg weight 0.64 g, 37 week egg weight -0.51 g and egg production to 273 d -1.83 eggs.
