Measuring aggressiveness in growing pigs in a resident-intruder situation

Studies concerning aggression after mixing unfamiliar pigs have shown that there is a great variability in the levels of aggression shown by individual pigs. This study examined whether individual aggressiveness can be measured in a resident-intruder situation and whether it is a stable characteristic of individuals, which does not simply reflect the age or sex class of the animal. These latter requirements are of fundamental importance in establishing the existence of individual personality or temperament characteristics in animals. The research was carried out in three datasets, with a total of 218 pigs, females and entire males, at the age of 7 and 11 weeks, For the test, individual pigs were isolated in one half of their home pen, and an intruder pig was introduced. This pig was 2-3 weeks younger than the resident pig. The time from when the resident first made contact to when it attacked the intruder pig was used as a measure of aggressiveness. If the resident did not attack, the test was terminated after 3.5 min. The test was repeatable across two consecutive days as well as across four weeks. Aggressiveness was found to be unrelated to characteristics of the test pigs, such as sex, age, body weight and body weight ranked within litter. Attack latency was not affected by the sex of the intruder pig, If the intruder was less than half the body weight of the test pig, it was less likely to be attacked. Considerable variation was found within as well as between litters, The importance of the nature of the test arena, and implications of the duration of the test are discussed, Using attack latency as a measure of aggressiveness and a relatively short time limit, the test provides a useful tool for measuring aggressiveness without compromising the welfare of the animals involved. (C) 1997 Elsevier Science B.V.