Introduction Focussing on animal we

Introduction
Focussing on animal welfare aspects, individual pig behaviour instandard situations of commercial pig production is becoming more and more important. In the daily routine work of pig farms, the mixing of unacquainted pigs is a common occurrence (Ismayilovaet al., 2013). To establish a stable rank order in the group, the pigs fight each other. The stable hierarchy is usually achieved at the third day after re-housing and is needed to prevent permanent∗
stress in the groups (Meese and Ewbank, 1973). However, the spe-cific fighting beha viour of pigs shows a large variation betweenin dividuals. Here, animals with enhanced aggressive behaviour can influence the health, welfare as well as the weight gain of especially low-ranking pigs (Tan et al., 1991; Tuchs cherer and Manteuffel, 2000). Former investigations had estimated moderate heritabilities of aggressive and submissive traits (Løvendahl et al.,2005; Turner et al., 2008,2009; Stukenborg et al., 2012). Therefore,knowledge regarding the behaviour of pigs in agonistic in teractionsgives the opportunity for breeding of calm and less aggressive ani-mals (Kanis et al., 2005; D’Eath et al., 2009). However, agonisticinte ractions at different ages are not easy to measure due to the time-consuming and lavish observation methods mostly by video