Intra-Group Lethal Gang Aggression in Domestic Pigs (Sus scrofa domesticus)

Abstract

Intraspecific coalitional aggression is rare among all species, especially within stable social groups. We report here numerous cases of intraspecific lethal gang aggression within stable groups of domestic pigs. The objective was to describe this extreme aggression and to identify potential causes. Management data were collected from farms with (n = 23) and without (n = 19) gang aggression. From one farm, 91 victims were assessed for skin injuries and body condition score. Lethal gang aggression was significantly associated with deep straw bedding, which may be related to various other factors. Gang aggression tended to occur more in winter, and was unrelated to genetic line, breeding company, group size or feed type. It occurred equally in female-only and mixed sex groups (male-only groups were not represented), from around eight weeks of age. Injuries typically covered the whole body and were more severe on the front of the body. Victims who survived had a lower body condition score and fewer injuries than victims found dead. There are still many unknowns as to why this abnormal social behaviour occurs and it deserves further research attention, both for its applied relevance to animal welfare as for the evolutionary background of lethal gang aggression.

From Animal Personality to Animal Individuality in Farm Animals – A Review

“…It has been found that gang aggression is neither related to the genetic lineage of the pigs nor dependent on the type of feed and occurs independently of sex. This type of behaviour has never been studied before because it was thought to be very rare (Camerlink et al, 2020). Nevertheless, it has been shown that, despite their seemingly marginal nature, these behaviours have a significant impact on animal performance on farms where they occur since they lead to mortality in growing pigs (Camerlink et al, 2020).…”

“…This type of behaviour has never been studied before because it was thought to be very rare (Camerlink et al, 2020). Nevertheless, it has been shown that, despite their seemingly marginal nature, these behaviours have a significant impact on animal performance on farms where they occur since they lead to mortality in growing pigs (Camerlink et al, 2020). The above observations may be evidence of the role of individualised yet infrequent personality traits predisposing some animals to leadership in so-called pig gangs that attack individuals lower in the hierarchy.…”

Selection for social genetic effects in purebred pigs improves behaviour and handling of their crossbred progeny

“…In commercial pig production, reducing the expression of harmful social behavioural traits, such as ear manipulation and tail biting and increasing the positive response to human handling, are of major interest. Ear manipulation and tail biting represent the main forms of harmful social behaviour in pigs [ 1 ], as they cause injuries, suppress immunocompetence, decrease growth rate and feed efficiency, and increase the risk of mortality [ 2 ]. As such, they significantly compromise animal welfare and economic and environmental sustainability.…”