“Genetic Influences on the Behavior of Chickens Associated With Welfare and Productivity § Selection Involving Production Traits”, 2014 (; similar):
Many behaviors in poultry can be modified by genetic selection. Selection of laying hens for maximum egg production had the unfortunate side effect of increased rates of beak inflicted damage on other birds. Selective breeding has eliminated broodiness and has either increased or decreased other behaviors, such as hysteria, fearfulness, appetite in broilers, social dominance, ability and damage to other birds.
Genetic selection can be used to reduce behaviors that cause welfare problems. However, it must be approached with caution to avoid unintended consequences that would be detrimental to welfare. A calm, docile bird that appears behaviorally calm, may take longer for its heart rate to return to normal after it is frightened.
The use of group selection instead of single-bird selection can be effectively used to reduce undesirable behaviors such as feather pecking and to maintain high egg production. An entire group of birds is selected instead of selecting individuals.
[Keywords: feather pecking, group selection, poultry, welfare]