The pig's nose and its role in dominance relationships and harmful behaviour

Affiliative behaviour may have an essential role in many behavioural processes. Gently nosing between group members occurs in almost all social behavioural processes of pigs (Sus scrofa), but the reasons for its performance are unclear. We examined whether nosing between pigs was related to dominance relationships or harmful behaviours such as manipulation of the tail using 80 crossbred pigs. Both males and females, housed in straw pens, were studied at 8 weeks of age (10 pigs/pen). Dominance ranks were determined by a feed competition test. The behaviour of 64 focal pigs was observed for 2 h per pig in total. Pigs nosed their pen mates on average 36 ± 3 times within 2 h, and nosing behaviour mainly consisted of nose-to-nose contact, nosing the head and nosing the body, rather than nosing the ear, groin, tail or ano-genital region. These gentle pig-directed nosing behaviours, i.e. gently touching another individual with the snout, was here defined as social nosing. Dominance relationships did not influence the amount of nosing given or received. Social nosing was largely unrelated to harmful behaviour. Nosing the tail correlated with tail biting (rs = 0.37), but only 0.3 percent of social nosing was followed by this behaviour. Pigs which delivered much nosing did not receive less aggression, and nor did they receive a heightened amount of nosing in return. We suggest that pigs may nose each other for social recognition, as affiliative behaviour, to gain olfactory signals, or to satisfy an intrinsic need to nose. In conclusion, social nosing in pigs was largely unrelated to harmful behaviours, was not related to dominance relationships and should remain largely unaffected by efforts to minimise harmful behaviours in farming systems.