Do pigs have altruistic behaviour based on cognitive empathy?

BACKGROUND: Altruistic behaviour is commonly defined as actions that benefit others at a potential cost to oneself and, in animal research, is typically inferred when individuals assist conspecifics without immediate personal gain. In pigs, altruistic behaviour associated with cognitive empathy remains an understudied area. In the present study, altruistic behaviour was operationally defined as a pig voluntarily sacrificing its own access to a food reward to alleviate a peer’s distress. We investigated whether pigs adjust their own behaviour in relation to the emotional state of others in a manner consistent with cognitive empathy-based altruism. METHODS: A total of 180 piglets were assigned to 90 test units, which were randomly allocated to one of nine treatment groups in a 3 × 3 factorial design. In this design, both the active and passive pigs could receive one of three treatments (reward: food, punishment: mild electric shock, or no treatment) after the active pig pressed the button. Behavioural manifestations and changes in heart rate of both active and passive pigs were recorded for one hour. RESULTS: The results showed that when passive pig was punished, active pig reduced the button presses to alleviate passive pig’s pain, even though active pig itself would receive a reward (p < 0.01). CONCLUSION: This behaviour suggests that pigs are able to relate their own behaviour to the emotional distress of their peers and act to alleviate the distress, demonstrating altruistic behaviour driven by cognitive empathy.