Selection with restriction in a poultry breeding scheme with different selection procedures in both sexes: Correlated responses

Abstract

1. Mass selection in two replicate lines of Leghorn chickens was practiced for low 20‐week body weight in males and by an index designed to reduce age at first egg, body weight at 20 weeks and maintain a constant early egg size in females.

2. Selection responses in body weights of hens at 40 and 60 weeks of age, as well as in average egg weight of all eggs, egg number, egg mass and feed conversion at the above ages are given for 5 generations of selection.

3. Estimation of genetic responses were made separately for selection on males (M _i ) and females (F _i ) using control groups of hens from matings between females with an index near the population average and either males with body weight near the population average (Cl) or the selected males within lines (C2).

4. Total genetic response to selection of both parents (CR _i ) showed an expected decline in body weights of hens, small changes in egg weights and egg numbers, and an improved feed efficiency.