Consistency of aggressive temperament in domestic pigs: The effects of social experience and social disruption

Abstract

Resident-intruder (R-I) tests can be used to measure the aggressive temperament of domestic pigs (Sus scrofa), and have previously been shown to predict the severity and persistence of aggression when unfamiliar pigs are mixed. To study the consistency of individual differences in aggressiveness over time, 112 pigs (eight from each of fourteen litters) were given two R-I tests at each of three ages (46, 80, and 113 days). Pigs were R-I tested singly in an arena within the home pen, where a smaller unfamiliar intruder pig was introduced to a resident pig. Latency to the first attack by the resident was recorded, and the test was stopped as soon as an attack occurred, otherwise the test lasted five minutes. Pigs from eight of the litters used here had been allowed to mix with another litter prior to weaning (days 10-30; socialised), while pigs in six litters remained in littermate groups (control). To determine whether consistency would survive the effects of social disruption, pigs were mixed into new groups on two occasions between the first and second test, then remained in these groups until the third test. Evidence of consistency was found, despite the social disruption. Socialised pigs were more aggressive than controls, females were more aggressive than males, and certain litters were more aggressive than others. After adjusting for these, consistent differences between individuals were still evident. Consistency was higher between the second and third tests compared to the first and second, possibly because of stable group membership or the effects of age or experience. In support of the idea that social experience improves consistency, socialised pigs were more consistent than controls throughout. Evidence of consistent individual differences in aggressive temperament suggests that breeding or changes to early life experiences could have a long-lasting influence on aggressive behaviour in pigs.

Aggressiveness as a component of fighting ability in pigs using a game-theoretical framework

“…As such, the attack latency in the RI test showed considerable variation between individuals and a moderate correlation within individuals. This repeatability adds to the existing studies that indicate that the RI test reflects aggressiveness as a personality trait (Carere, Drent, Privitera, Koolhaas, & Groothuis, 2005;D'Eath, 2004). The evidence for a link between animal personality and contest behaviour has recently been reviewed (Briffa et al, 2015).…”

“…The RI test is an established test in behavioural research that is undertaken to obtain a quantifiable measure of individual aggressiveness (Koolhaas et al, 2013). In pigs the RI test has been shown to be consistent over time (D'Eath, 2004) and to be predictive of aggressiveness when animals are mixed with multiple unfamiliar animals . In the test a 'resident' was kept individually in a separate part of its home pen.…”

“…In this study we assayed individual differences in aggressiveness, using the established residenteintruder (RI) test , which provides a measure of aggressiveness that is consistent over time (Clark & D'Eath, 2013;D'Eath, 2004). The resultant measure of attack latency provides an unambiguous, quantifiable measure of aggression in a format that can be interpreted within an RHP framework.…”

Network characteristics and development of social structure of agonistic behaviour in pigs across three repeated rehousing and mixing events

“…This habituation effect could be combined with a learning process. The animals learn from previous fight situations and the confidence gained from previous successes in agonistic interactions in particular has an important impact on the future behaviour of the animals (Otten et al, 1997;D'Eath, 2004). However, also an increasing maturation of the animals can be seen as an explanation.…”

Relationship between behavioural tests and agonistic interactions at different age levels in pigs

“…More dominant pigs as weaned pigs were less involved in agonistic interactions in new mixing situations at re-housing in the growing stable. D'Eath (2004) emphasised this statement in their investigation that success in fighting had a long-lasting effect on the dominance status of the individual pig in a new mixed group. Also Otten et al (1997) stated that the former rank position in a group influenced the agonistic interactions in the new group.…”