Abstract
Anxiety is a physio-psychological state anticipating an imminent threat. In social mammals it is behaviorally expressed via displacement activities and buffered via affiliation. Anxiety research on domestic pigs (Sus scrofa) has mostly focused on abnormal/stereotypic behavior associated with intensive farming. We investigated how anxiety is expressed and modulated in semi-free ranging pigs, in natural habitats. Owing to pigs' socio-cognitive complexity, we posited that displacement activities, if such, would increase after a (stressful) intra-group aggression (Prediction 1), be reduced by affiliation (Prediction 2) and influenced by individual/contextual factors (Prediction 3). From 224 videos recorded on adult individuals (Mean ± SD/subject: 4.84 ± 1.85 h) at the “Ethical Farm Parva Domus” (Turin, Italy), we extracted possible displacement activities (vacuum-chewing, scratching/body-rubbing, head/body-shaking, and yawning) in four 3-min conditions: before (BA) and after aggression events, in the absence (AA) or presence (AP) of post-aggression affiliation, and a matched-control (no event; MC). We conducted a minute-by-minute analysis in AE/AA and assessed the effect of subjects' involvement in a conflict (aggressor, aggression's recipient, bystander). All activities were higher in AA than in BA condition—thus being anxiety markers—and all of them decreased to baseline levels in AP, faster compared to AE. Hence, anxiety behavior in pigs was socially buffered. Intriguingly, anxiety behavior was expressed significantly more by bystanders than opponents, which suggests that pigs may be able to anticipate imminent threats. By highlighting how anxiety is managed under extensive farming, this study contributes to the understanding of pig welfare and biology.
Highlights
In its broader definition, anxiety is an affective state that in both humans and other mammals is characterized by tension and/or agitation and is often behaviorally expressed in association with a physiological stress response [1,2,3,4,5]
The yawning frequencies were significantly different across the conditions considered: before the aggression (BA; Mean ± SD: 0.012 ± 0.032), after the aggression in the absence of affinitive contact (AA; 0.080 ± 0.134), after affinitive contact (AP; 0.018 ± 0.055), and in the Matched Control (MC; 0.010 ± 0.037) (Friedman test: N = 44, χ 2 = 33.224, df = 3, p < 0.001)
The results of this study show for the first time that certain behaviors, part of the typical repertoire of Sus scrofa, can express anxiety, be buffered by social contacts, and possibly anticipate an imminent threat
Summary
Anxiety is an affective state that in both humans and other mammals is characterized by tension and/or agitation and is often behaviorally expressed in association with a physiological stress response [1,2,3,4,5]. Nonpathological anxiety is commonly present in a mammal’s life as a psychological, physiological, and behavioral response that helps the subjects to deal with unexpected or challenging situations [15]. Owing to this basic function, convergence in some anxiety related behaviors has been observed between humans and non-human mammals [16]. The anxiety response to aggression can be present but may vary depending on the role played by individuals in the conflict [e.g., pigs [19]; rats, Rattus norvegicus [20]; various nonhuman primate species [17, 21,22,23,24,25]]. The behavioral expression of anxiety in agonistic contexts is necessary to ensure effective communication between individuals within a society and allow the enactment of social buffering measures [20, 31, 32]
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