Tail Biting and Feather Pecking: Using Genomics and Ethology to Explore Motivational Backgrounds

It is well known that abnormal animal behaviour is affected by both environment and genetics. This thesis aimed to use behavioural observations as well as gene expression measurements to explore how animals that perform and receive tail biting (pigs) and feather pecking (laying hens) differ from individuals that are not involved in these behaviours. In study I, the results suggested that tail biting is related to other abnormal behaviours. Pigs performing a high frequency of tail biting focused on abnormal behaviours that included oral manipulation (such as ear and bar biting), whereas those performing less tail biting showed a wider variety of different abnormal behaviours. In study II and III, many genes were differently expressed when neutral pigs were compared with tail biters and receivers, all housed in the same pen, as well as when compared to control pigs housed in a pen with no tail biting. This suggests that the neutral pigs had a phenotype that made them somewhat resistant towards performing and receiving tail biting. Behavioural data, in combination with information on the functions of these differently expressed genes, indicated that this difference in behaviour was due to the neutral pigs being less pig-directed in their behaviour. The focus on pigs which remain neutral in the outbreak is a new approach in tail biting studies. The gene expression data further suggested that selection for production may unintentionally have created pigs that perform and receive more pig-directed abnormal behaviour. In study IV, the functions of many of the 16 genes differently expressed between feather pecking hens, victims and control birds, support earlier hypotheses about feather pecking being linked to nutrition/feeding and immune mechanisms. In summary, this thesis provides both behavioural characteristics and lists of genes that strengthen earlier reported results as well as give new suggestions about the biological mechanisms underlying tail biting and feather pecking behaviour.