Once bitten, twice shy: Aggressive and defeated pigs begin agonistic encounters with more negative emotions

Abstract

Aggression between unfamiliar commercial pigs is common and likely invokes strong emotions in contestants. Furthermore, contest outcomes affect subsequent aggressive behaviour, suggesting a potential lasting influence on affective state. Here we used a combination of qualitative and quantitative methods to assess the emotional expression of pigs in agonistic encounters. We investigated how recent victory or defeat influences emotions expressed in a subsequent contest, and the role of aggressiveness as a personality trait in emotional expression. We observed the pre-escalation contest behaviour (second contest; age 13 wks) in animals of different aggressiveness (categorised using two resident intruder tests as Agg+ or Agg-, age 9 wks), which had recently won or lost a contest (first contest; 10 wks). We measured gaze direction and ear position. Observers watched video clips of the initial 30 s of the second contest and evaluated the emotional expression of 57 pigs (25 contest 1 winners, 32 contest 1 losers) using qualitative behavioural assessment (QBA) with a fixed list of 20 descriptive terms. QBA identified three principal components (PCs), accounting for 68% of the variation: PC1 (agitated/tense to relaxed/content), PC2 (fearful/aimless to confident/enjoying) and PC3 (listless/ indifferent). Agg- pigs and males showed a more positive emotionality (PC2). PC1 and PC3 were unaffected by first contest outcome and aggressiveness. Agg+ pigs were more likely to hold their ears back (X 2 =7.8, p = 0.005) during the early contest period. Differences in attention were detected in the contest outcome × aggressiveness interaction (χ 2 4.3, p = 0.04), whereby approaching the opponent was influenced by winning and losing in the Agg- pigs only. QBA and gaze behaviour reveal differences in emotional valence between pigs of different aggressiveness: less aggressive pigs may be more susceptible to the emotional impact of victory and defeat but overall, more aggressive pigs express more negative emotionality at the start of agonistic encounters.

Pattern Mining-Based Pig Behavior Analysis for Health and Welfare Monitoring

“…Pig24 was the most frequent aggressor, followed by Pig17, Pig18, Pig13, Pig10, and Pig7. This observation suggests that Pig15 might be in a compromised state, potentially due to sickness, injury, or physical vulnerability, which makes it more susceptible to attacks from its peers [119]. Even though Pig15 exhibited aggression by attacking only Pig18, the extent of the attack was relatively mild compared with other instances of aggression.…”

A systematic approach to defining and verifying descriptors used in the Qualitative Behavioural Assessment of sows

“…A good agreement was reached on PC2 that is more related to the arousal of emotions. The valence-arousal interpretation of emotional affect is frequently used in animal welfare and behaviour research (Mendl et al 2010 ), and common across QBA studies in both pigs (Wemelsfelder & Millard 2009 ; Temple et al 2013 ; Oldham et al 2021 ) and other species (Diaz-Lundahl et al 2019 ; Cooke et al 2022 ; Travnik et al. 2022 ).…”