Rub ‘n’ roll – Pigs, Sus scrofa domesticus, display rubbing and rolling behaviour when exposed to odours

Abstract

Pigs are regarded as having a highly developed sense of smell, although scientific information on the topic is sparse. Here, we describe two behaviours unexpectedly observed in a study assessing pigs’ responses to odours and not previously reported in pigs. The study included 192 pigs of commercial breeds, tested in pairs with 12 different odours of non-social origin: 8 essential oils and 4 synthetic perfumes, plus an odourless control. Each odour was tested 24 times in triads of three odours. The results showed that, when exposed to odours, pigs display rubbing and rolling behaviour. Pigs displayed rubbing behaviour in 18 % of all odour exposures. Rolling behaviour was less frequent and displayed 7 times by five different pig pairs. Rubbing was always displayed following sniffing behaviour, and after a rubbing event, the pigs either performed sniffing behaviour (86.1 %), attempts at rolling (8.8 %) or a rolling event (5.1 %). Both males and females performed the rubbing behaviour (61 % female, 39 % male, Wilcoxon signed-rank test: W = 2199, P > 0.1), rolling behaviour (71 % female, 29 % male) and attempts at rolling (62 % female, 38 % male). Overall, essential oils (lavender, thyme, blood orange, aniseed, cedarwood, cinnamon bark, ginger, and pine) elicited more of the behaviours than the synthetic perfumes (vanilla, musk, apple, and jasmine) or the odourless control. All odours elicited rubbing whereas only four odours (blood orange, ginger, lavender, and pine) elicited rolling. Scent-rubbing/scent-rolling is a well-known behaviour in both wild (e.g., wolves and coyotes) and pet (e.g., cats and dogs) carnivores, although the function is not clear. This is the first report of rubbing and rolling as a response to an odour in pigs. The motivation for performing these behaviours is unknown but may include skin care, comfort behaviour or marking behaviour. Further studies allowing pigs physical access to rub and roll in different odours may elucidate the underlying motivation.