Effects of genetic group selection against mortality on behavior and peripheral serotonin in domestic laying hens with trimmed and intact beaks J. Elizabeth Bolhuis a, ⁎, Esther D. Ellen b , Cornelis G. Van Reenen c , Johanna De Groot a , Jan Ten Napel d , Rudie E. Koopmanschap a , Ger De Vries Reilingh a , Koen A. Uitdehaag b , Bas Kemp a , T. Bas Rodenburg b a Adaptation Physiology Group, Wageningen Institute of Animal Sciences, Wageningen University, P.O. Box 338, 6700 AH, The Netherlands b Animal Breeding and Genomics Centre, Wageningen Institute of Animal Sciences, Wageningen University, P.O. Box 338, 6700 AH, The Netherlands c Cluster Animal Welfare, Animal Sciences Group, P.O. Box 65, 8200 AB Lelystad, The Netherlands d Animal Breeding and Genomics Centre, Animal Sciences Group, P.O. Box 65, 8200 AB Lelystad, The Netherlands abstract article info Article history: Received 9 October 2008 Received in revised form 5 March 2009 Accepted 23 March 2009 Keywords: Fear Stress Feather pecking Cannibalism Group selection 5-HT transporter Platelet Survival Laying hens Anxiety Severe feather pecking is a maladaptive behavior in laying hens that may result in cannibalism and ultimately death of the victims. Selection methods in which the genetic effect of an animal on the survival of its group members is taken into account, i.e. ‘group selection’, have been shown to be very effective in reducing mortality due to feather pecking and cannibalism in laying hens. It has been suggested that fearfulness and serotonergic functioning are involved in the causation and development of feather pecking. We investigated effects of selection based on survivability in non-beak trimmed groups on fear-related behavior and peripheral 5-HT concentration and uptake in hens with trimmed or intact beaks, in a 2 × 2 factorial arrangement. Hens from the second generation of the low mortality line showed less fear-related behavior than control line hens. In addition, they displayed higher whole blood 5-HT concentrations and a lower platelet 5-HT uptake, indicating differences in functional activity of the 5-HT system. Beak trimming resulted in lowered levels of fear, and in a reduction of feather damage. Hens with trimmed and intact beaks did, however, not differ in peripheral 5-HT. The results imply that fearfulness and 5-HT activity are related to feather pecking without distinguishing between cause and effect. However, given that selection altered fear- related behaviors and peripheral 5-HT concentration and uptake, whereas beak trimming affected fearfulness and feather damage, but not 5-HT parameters, we suggest that peripheral 5-HT activity might reflect the predisposition to develop severe feather pecking under adverse conditions in laying hens. © 2009 Elsevier Inc. All rights reserved. 1. Introduction Laying hens kept under commercial conditions frequently develop severe feather pecking, i.e. vigorous, compulsive pecking at and pulling out of feathers of group members, leading to feather damage and feather loss [1]. Severe feather pecking may result in denuded body areas, which can trigger the development of cannibalism and, ultimately, may lead to the death of the victims [2]. Feather pecking is generally thought to be a form of pecking behavior, either derived from foraging or dustbathing, that is redirected from the litter to the plumage of conspecifics [3,4]. Multiple factors seem to facilitate the development of severe feather pecking and cannibalism, such as sub- optimal housing or rearing conditions [5,6] and inadequate feeding strategies [7]. Not all individuals seem to be predisposed, however, to develop feather pecking or cannibalism under adverse circumstances, as there are clear individual differences, both between and within genetic lines, in the occurrence of these damaging behaviors [8–10]. Various studies have therefore attempted to identify individual behavioral and physiological characteristics of feather peckers and cannibalistic hens as possible predisposing factors (e.g. [11–13]). Several authors have suggested a link between feather pecking and/or cannibalism and fearfulness [14–16]. For instance, feather damage was found to be associated with fear in caged hens [17–19]. It was initially assumed that the pecked hens had become more fearful because of the discomfort and pain inflicted by the pecks [18,19]. Others, however, proposed that fear may also be involved in the expression of feather pecking, as fear-related behavior was correlated with severe feather pecks delivered [20]. Moreover, it has been shown that birds that developed feather pecking as adults already differed in fear responses at a young age [21], suggesting that fearfulness is a predisposing underlying trait rather than (only) a result of feather pecking. These behavioral characteristics of hens with a strong predisposition to develop feather pecking may originate from under- lying differences in (neuro)physiology. In the search for physiological characteristics of feather peckers, serotonergic activity has been suggested to play a key role [22]. Distribution of serotonergic fibers in Physiology & Behavior 97 (2009) 470–475 ⁎ Corresponding author. E-mail address: liesbeth.bolhuis@wur.nl (J.E. Bolhuis). 0031-9384/$ – see front matter © 2009 Elsevier Inc. All rights reserved. doi:10.1016/j.physbeh.2009.03.021 Contents lists available at ScienceDirect Physiology & Behavior journal homepage: www.elsevier.com/locate/phb