Reimert, I., Bolhuis, J. E., Kemp, B. 2012. Indicators of positive and negative emotions and emotional contagion in pigs. Physiology & Behavior 109, 42-50.
For the welfare of group-housed animals, such as pigs, the emotional state of an individual pig is relevant, but also the extent to which pen mates are affected by the distress or pleasure of other...