Social sham chewing in sows?

In this short communication, we describe chewing behaviour in sows with no apparent edible substrate in their mouth as a potential social behaviour. Chewing in sows during interaction with unfamiliar sows was unexpectedly observed in a study assessing social abilities and damaging behaviours in group-housed dry sows. Such chewing was observed frequently and performed by almost all sows. To our knowledge, this behaviour has not been described previously in a social context in pigs, but rather as an oral stereotypic behaviour related to chronic hunger. We describe the behaviour in its social context and speculate on reasons for its occurrence in that context.