Selection of putative indicators of positive emotions triggered by object and social play in mini-pigs

Positive welfare is more than the absence of negative experiences. Nevertheless, there are few feasible animal-based measures for positive welfare. This study aimed to investigate whether object and social play behaviours in pigs, which is believed to trigger positive emotions, is linked to peripheral oxytocin and/or serotonin changes over time. Moreover, the study examines the relationship between tail movement, play behaviour, and peripheral levels of oxytocin and serotonin in animals that have the possibility to play, along with the approach towards humans and the difficulty/ease of working with the animals. At six months old, 10 mini-pigs from the Play group participated in one or two play sessions per day for three weeks. Eight mini-pigs from a Control group did not participate in play sessions. For each first play session, blood was sampled before the play session (T0) and 5–10 min after the play session ended (T1). The same procedure was performed each day for three weeks. For the Control group, blood samples were drawn at the same times as the experimental group, the following day. Results showed a Play session effect on oxytocin, where a significant difference was observed for time (Chi-Square = 3.88, DF = 1, p = .05) and for group*time interaction (Chi-Square = 5.65, DF = 1, p = .02): in the Control group, T1 was significantly higher than T0 (p