FIGHTING BETWEEN UNACQUAINTED PIGS - EFFECTS OF AGE AND OF INDIVIDUAL REACTION PATTERN

Two experiments were conducted on fighting between unacquainted pigs. The first investigated the effect of age. The second experiment investigated correlations between the way piglets react to non-social novel stimuli and to social stimuli (i.e. strangers). In Experiment 1, repeated paired encounters were staged between female piglets of three different ages (1, 5 and 9 weeks, ten pairs of each age), matched for weight. Age did not influence the probability that the piglets would fight during the tests. However, 1-week-old animals fought for a shorter time and in a more offensive way. One-week-old piglets fought less on the second meeting, whereas the older piglets tended to fight more. In Experiment 2, 29 7-week-old female piglets were first exposed to novel objects in a novel pen and then confronted a small male in a neutral arena. Behaviour and heart rate were measured during the non-social novelty test. Individuals differed considerably in their reactions to the nonsocial novel stimuli. Nine of the piglets did not fight in the opponent test, whereas the rest. all commenced fighting within 8 min. There were no clear relations between the reactions in the novelty test and the subsequent probability of engaging in fights. In conclusion, neither age nor reactions to non-social stimuli were good predictors of whether a pig would engage in fights with strangers. However, age determined the length and course of the fighting.