[Genetical differences in pecking behaviour among hens in loose housing]

abnormal behaviour aggressive behaviour alojamiento de animales animal housing body parts cama (animales) comportamiento agresivo comportamiento anormal comportement agressif comportement alimentaire comportement anormal damage establos feathers feeding habits gallina ponedora genetic variation introduced breeds layer chickens litter for animals logement des animaux mortalidad mortalite mortality noruega norway partes del cuerpo partie du corps plumas plume poule pondeuse race introduite razas naturalizadas selection criteria stalle stalls