Progress of aggressive pecks and several behavioral traits in rank-order-instable cage groups in laying hens

Abstract

Higher animals establish a rank-order, which provides advantages to the social life of these animals. The rank-order moderates aggression and decreases stress-based frustration. Laying hens kept in cages are normally replaced with new ones after they die. This results in conflict in the rank-order of the animals, particularly in adult hens depending on breed and line and, as a result, causes violation among animals. This is a stress situation, which can negatively affect welfare of the animals. In this study, the effect of instable rank-order on aggressive pecking and some behavioral traits was investigated in laying hens. Fourty eight white Lohmann LSL laying hens were used as animal material. The stocking rate was 4 laying hens in all cages, except for six cages in which a stable rank-order was formed with animals who came from different cages. The behavioral traits of aggressive pecking, feeding, drinking, feather pecking, cage pecking, standing and recumbency were monitored. A significant difference in aggressive pecking was found between stable rank-order and instable rank-order groups. The laying hens in instable-rank-order group showed more frequently aggressive pecking than those in rank-order-stable group. However, the progress of aggressive pecking during the experimental period indicated an elevation of aggressive pecking in both of the groups. The reason for increased aggressive pecking in the rank-order-stable group was thought to be due to the threatening with noise of the animals in the rank-order-instable group. Feather pecking was significantly higher in the instable rank-order group than in the stable rank-order group, indicating the frustration of the hens in the former group. Feather pecking is normally defined as a comfort behavior, but is not observed in every situation. This behavior could be classified as a "sparking over activity".