Thesis subject

Social hierarchy formation in weaned pigs – An agent-based approach - Marieke van der Laak

Mixing after weaning is common practice in commercial pig farming. Agonistic behaviour is observed in the pen shortly after mixing, in which pigs establish dominance relationship from which a social hierarchy on group level is formed. The aim of this study was to identify key behavioural processes in pigs that lead to a social hierarchy formation.

With a literature study, a theoretical framework was created to identify the main behavioural processes. Main processes during social hierarchy formation are initiation of a fight, fighting and behaviour after a fight. Initiation of a fight includes meeting, assessing and attacking other pigs. The sub processes of fighting are starting a fight, enduring a fight and ending a fight. Behaviour after a fight includes behaviour directly after a fight and on subsequent encounters. The theoretical framework was implemented into an agent-based model that represented a pen with weaned piglets and simulated fights between pigs until a social hierarchy was formed. The effects of fighting skills and fighting intensity of pigs were tested on the frequency of fights on group and individual level.

Modelling results showed that fighting skills based on fixed individual characteristics before mixing result in similar output as when fighting skills are based on variable experience after mixing. Development of fights was comparable to empirical data in literature. This suggests that fighting skills during a fight does not highly affect the developments of fights during social hierarchy formation. An increased fighting intensity during fighting, however, did lead to an increased number of fights and a faster formation of hierarchy. In groups with low fighting intensity, dominance relationships are established by peaceful interactions rather than fighting. The developed model is a simplified representation of the complex process of social hierarchy formation, which can serve as a basis to further study processes underlying social hierarchy formation.

Student: JH van der Laak

Supervisor: ing I Boumans, MSc

30 Ects