UNDERSTANDING ASSESSMENT STRATEGIES DURING AGGRESSIVE ENCOUNTERS BETWEEN PIGS

Regrouping unfamiliar pigs is a common and unavoidable on-farm practice and results in aggressive behaviour with dominance hierarchies formed through vigorous fighting. This is a considerable welfare concern.

There is substantial variation in the amount of aggression that individual pigs show upon encounter, which suggests that pigs are able to make decisions about whether to fight or not. To date it has been assumed that pigs are capable of making fighting decisions based on assessment of their opponent. This may however not be the case and instead pigs may fight based on assessment of their own strength only.

The assessment strategy used has major implications for the costs of fights, such as injuries and energetic costs, and how we might try to manage aggression. Moreover, it is unknown how aggressiveness as a personality trait affects pigs’ assessment strategy or their ability to win a fight. Game theory offers a useful framework to address these knowledge gaps.

We aim to reveal the assessment abilities of pigs, to determine how personality traits affect this and whether experience (including early life experience) can encourage a shift towards an assessment strategy that minimises the costs of fighting. To date we have shown that escalated fighting is not a prerequisite for weight-matched pigs to establish a dominance relationship.

An aggressive personality increases the likelihood of initiating aggression but does not increase the chance of winning when a contest does not escalate into a fight. Furthermore, increased time dedicated to opponent investigation and non-damaging display can greatly reduce the risk of escalation. Subsequent analyses will characterise the assessment strategy used by pigs and the role that previous experience of aggressive interactions has on the development of assessment abilities.

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