AGONISTIC INTERACTIONS AND PHYSIOLOGICAL REACTIONS OF TOP-AND BOTTOM-RANKING PIGS CONFRONTED WITH A FAMILIAR AND AN UNFAMILIAR GROUP - PRELIMINARY-RESULTS

Four trials were carried out, where in each trial during a selection r est two groups of growing pigs (12 weeks old) with nine animals each w ere randomly formed. After a week, the top (TR) and bottom (BR) rankin g pig from each group was isolated and kept under single housing condi tions. At the age of 15 to 16 weeks, the test animals were confronted once with the familiar and once with the unfamiliar group. During the 10-h social confrontation test, agonistic behaviour (agonistic interac tions, individual dominance values) and physiological stress reactions (epinephrine, norepinephrine, cortisol, heart rate) were investigated simultaneously. The social confrontation of a pig with a familiar or an unfamiliar group caused very frequent agonistic interactions during the first 30 min. This behaviour was accompanied by a rapid increase of the heart rate and the plasma catecholamine concentrations and a de layed increase of cortisol. TR pigs elicited more agonistic interactio ns during the first 30 min and displayed higher plasma catecholamine c oncentrations. Additionally, TR animals showed significantly higher do minance values during the 10-h testing situation compared to the BR pi gs. The confrontation of an animal with the unfamiliar group resulted in a more pronounced adrenocortical reaction compared to the confronta tion with the familiar group. In particular, the TR animals showed a d istinct increase of plasma cortisol during the first hour and a later bradycardia when they were confronted with the unfamiliar group. The p reliminary results presented in this paper indicate that pigs show dif ferent, but inconsistent behavioural and physiological reactions when they are confronted with a social group. The agonistic behaviour and t he physiological stress reactions during a social confrontation test a re still influenced by the former rank of the animal, even when the an imal was isolated under single housing conditions in the meantime for 2 to 3 weeks. (C) 1997 Elsevier Science B.V.