RECOGNITION IN SWINE - RECOGNITION THROUGH FAMILIARITY OR GENETIC RELATEDNESS

Intense aggression is the most common behavioural response when pigs f rom two different groups are put together. The triggering mechanism wh ich elicits the aggressive response appears to be the lack of recognit ion between the groups. However, recognition among animals may include elements of both previous exposure (familiarity) and genetic relatedn ess, which are confounded when re-grouping pigs. Two experiments were conducted to determine if recognition among piglets is based on famili arity alone or also involves genetic relatedness. In the first experim ent, 80 crossbred piglets from litters crossfostered within 3 days of birth were regrouped in pens of five pigs following weaning at 28 days of age. Each test group was composed of two siblings reared together (ST), an alien (non-related) piglet reared with the two siblings (AT), a sibling reared apart (SA), and an alien piglet reared apart from di e other group members (AA). Each pen was videotaped for 6 h following regrouping and the tapes were analyzed to determine the duration of fi ghting among pairs of pigs and the proportion of time spent lying in c ontact with other pigs. Dyads which had been reared together spent les s time fighting than those reared apart (67 vs, 252 s, respectively; P < 0.0001, general linear model). Related dyads spent a similar amount of time fighting as unrelated pairs (187 s and 131 s, respectively). Although 80% of the piglets demonstrated preferences for lying partner s during the observation, no consistent pattern existed across pens fo r specific pairings. In the second experiment, five litters were each divided into two groups within 72 h after birth and reared on separate sows. At 6 weeks of age pigs were paired either with a full sibling ( 16 pairs) or a non-sibling (14 pairs), either of which had been reared separately. Reunited full siblings spent a similar amount of time fig hting, within the 4 h following regrouping, compared to non-siblings ( 1425 vs. 1814 s, respectively). Based on the patterns of aggression ob served in the two experiments, recognition among young piglets appears to be based on familiarity gained through rearing associations, and d oes not involve genetic relatedness. (C) 1998 Elsevier Science B.V.