Applied Animal Behaviour Science 168 (2015) 24–30 Contents lists available at ScienceDirect Applied Animal Behaviour Science journal homepage: www.elsevier.com/locate/applanim Network characteristics and development of social structure of agonistic behaviour in pigs across three repeated rehousing and mixing events Kathrin Büttner ∗ , Katharina Scheffler, Irena Czycholl, Joachim Krieter Institute of Animal Breeding and Husbandry, Christian-Albrechts-University, Olshausenstr. 40, D-24098 Kiel, Germany article info Article history: Accepted 26 April 2015 Available online 12 May 2015 Keywords: Agonistic behaviour Pigs Social network analysis Group level abstract In commercial pig production, the mixing of unacquainted pigs is a standard procedure which leads to agonistic interactions with a wide range of individual pig behaviour. A reduction in these agonistic interactions positively affects animal health, welfare aspects and production parameters. With the help of social network analysis, insight into animal societies can be gained and structures of agonistic behaviour can be detected. The aim of the present study was to analyse how the general network properties (density, clustering coefficient, weakly and strongly connected components and centralisation) develop over three different rehousing and mixing events (weaned pigs, growing pigs and gilts). Therefore, the agonistic behaviour of the animals in the flatdeck pens, the growing and the breeding stables were recorded directly after mixing (in total 17 h of video observation for each pen). In total, 65 groups in the rearing area (flatdeck pens), 24 groups in the growing stable and 12 groups in the breeding stable were recorded. In contrast to the second and the third rehousing and mixing events, the results for the density and the clustering coefficient showed that in the agonistic interaction networks of the first mixing event the animals were very densely connected and therefore formed highly connected clusters, indicating that nearly all animals in a pen fought against each other during the observation period. The results for the weakly and strongly connected components suggest that agonistic interactions have a group-wide structure which is not immediately obvious in a dyadic analysis. Furthermore, the in-degree centralisation showed significantly smaller values than the out-degree centralisation at all three observed age levels, which suggests that the distribution of individuals initiating agonistic interactions was more skewed than the distribution of individuals receiving agonistic interactions. By quantifying the important aspects of group structure in different production stages, information based on social network analysis could help identify and understand the formation of behavioural patterns, e.g. agonistic interactions, tail biting and access to resources. © 2015 Elsevier B.V. All rights reserved. 1. Introduction The behaviour of farm animals both influences and is influ- enced by the presence and the behaviour of their conspecifics (Makagon et al., 2012). This means that in social networks an indi- vidual’s interactions with others are unlikely to be independent of the behaviours of others (Wasserman and Faust, 1994; Croft et al., 2005; Krause et al., 2007; Wey et al., 2008; Madden et al., 2009). Social interactions can, for example, affect the spread of new information or behavioural patterns within the groups. Espe- cially in farm animals, this transmission can lead to increased ∗ Corresponding author. Tel.: +49 431 880 5457; fax: +49 431 880 2588. E-mail address: kbuettner@tierzucht.uni-kiel.de (K. Büttner). behavioural problems such as feather pecking in laying hens or tail biting in pigs. According to Makagon et al. (2012), understand- ing how such behavioural patterns emerge and spread in a group of animals has many potential applications. For instance, knowing the social mechanisms underlying the spread of these and other behavioural problems could allow the development, improvement and implementation of prevention and intervention strategies. Beside these behavioural problems, regrouping of animals can also produce unstable social networks resulting in increased aggressive behaviour within the groups. Especially in commercial pig produc- tion, the rehousing and mixing of unacquainted pigs is a standard procedure which leads to agonistic interactions with a wide range of individual pig behaviour. Therefore, a more complete under- standing of the interaction between social structure and group stability has clear applications for managing aggression related to http://dx.doi.org/10.1016/j.applanim.2015.04.017 0168-1591/© 2015 Elsevier B.V. All rights reserved.