Groups of 17 sows each were grouped on day 40-50 of pregnancy and observed for two periods of 100 min each. They were assigned to two different treatments: (treatment S) grouped in the morning and observed immediately after; (treatment T) grouped in the morning after an injection of a tranquilizer (Azaperone) and observed immediately after. The animals in treatment S fought more frequently but with decreasing frequency. Fights amongst the T-sows were not eliminated and, moreover, increased during the second observation period. Despite these differences, the behaviour patterns displayed by the sows were essentially constant. Head-Head, Head-Body knocks, and Biting were the patterns more often used by the sow initiating the interaction in each treatment. The receiver animal responded most often with Head-Tilt and Retreat. The reasons for such differences in agonistic behaviour and the usefulness of tranquilizing the sows in relation also to their welfare are discussed.
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