Differential effects of positive and negative emotional contagion on environmental adaptability in pigs

This study aimed to investigate the effects of positive or negative emotional contagion on the environmental adaptability and pain sensitivity of the naïve pigs. In the study, 54 pigs were selected and paired into 27 test units, then assigned to the reward, punishment, and control groups (n = 9) randomly. In the reward or punishment groups, one pig in each pair was randomly chosen as the treated pig (TP), receiving either food rewards or electric shock treatments, while the other pig was the naïve pig (NP). The NPs did not have treatment or receive treatment information from the TPs. After the treatment, the paired pigs were allowed to interact for one hour. The paired pigs in the control group received no treatment and were allowed to interact with each other for one hour directly. Subsequently, the salivary physiological, open field, and pain sensitivity tests were performed. In the punishment group, the NPs showed elevated serotonin (P = 0.02) and amylase (P < 0.01), indicating negative emotion arousal. In the reward group, the NPs had higher cortisol (P = 0.01) and dopamine (P < 0.01), suggesting positive emotion arousal. The NPs in the punishment group spent less time in the central zone of the arena (P < 0.01), showing increased motivation to explore unfamiliar environments, while the NPs in the reward group spent more time in the central zone (P = 0.04), indicating reduced anxiety and improved environmental adaptation. Neither positive nor negative emotional contagion had a significant effect on the pain sensitivity of pigs. In conclusion, positive emotional contagion can improve pigs' adaptability to unfamiliar environments, while negative emotional contagion does not.