A tale too long for a tail too short? : identification of characteristics in pigs related to tail biting and other oral manipulations directed at conspecifics

Ursinus, W.W. (2014). A tale too long for a tail too short? Identification of characteristics in pigs related to tail biting and other oral manipulations directed at conspecifics. PhD thesis, Wageningen University, The Netherlands. Tail biting in pigs, i.e. the chewing on and biting in tails of conspecifics, is a multifactorial problem leading to impaired pig welfare and health and economic losses in pig farming. In many countries tail docking is used as a preventive measure, but there is increased societal concern about this practice. Therefore, there is an urgent need to understand, prevent, and reduce tail biting and other damaging behaviours directed at pen mates. The main aim of this thesis was to identify biological characteristics of barren and enriched housed pigs that relate to their tendency to develop these damaging oral manipulative behaviours. Tail biting started already early in life and pigs that displayed tail biting post-weaning seemed to stem from litters in which tail biting behaviour was already present. The onset of tail biting behaviour was different for individual pigs, and many pigs were not consistently tail biters throughout different phases of life. It was difficult to predict which pigs would develop tail biting based on their individual behaviour. Groups of pigs with tail biting problems were, however, more easy to identify by increased activity, and increased levels of pig and pen-directed oral manipulative behaviours. Subjecting pigs to an individual behavioural test showed that tail biters may be more fearful. Fearfulness in pigs appeared related to measures of the brain and blood serotonergic system. Moreover, measures of the blood serotonergic system seemed temporarily altered in tail biting pigs mainly during the phase of life in which they displayed this behaviour. Additionally, (tail) biting behaviour may be associated with higher (phenotypic and genotypic) production, such as higher growth. Growth of individual pigs can be affected by the other pigs in a pen. The heritable effect of one pig on the growth of another group member is referred to as an indirect genetic effect. Pigs with a relatively negative indirect genetic effect for growth displayed more biting behaviours, caused more tail damage and destroyed more of the available jute sacks. The presence of strawbedding or jute sacks as enrichment materials for rooting and chewing largely reduced damaging biting behaviours and, consequently, tail damage. Pigs that still develop tail biting behaviour in an enriched environment likely do so due to a (temporary) physiological problem, whereas in barren housed pigs the lack of suitable rooting and chewing material plays a large role. Tail biting behaviour in pigs thus seems to be caused by a variety of temporary states and more stable traits that influence their motivation to display foraging and exploratory behaviours. Therefore, the tale of (tail) biting behaviours in pigs needs a better understanding of underlying physiological processes. Preventing and reducing damaging biting behaviours in pigs requires a joint effort of science, industry and society to optimize housing conditions, feeding, management and breeding of pigs.