In several countries where intensive pig husbandry is carried out, the pregnant sows are kept tethered. Farmers, who are often frightened by aggression in their animals, state that such a method avoids high levels of competition among the individuals, with no risks for the growing foetuses. Nevertheless, tethering is certainly not optimal from the sow point of view, especially if we consider its welfare (Fraser, 1975; Stolba et al., 1983). On the other hand, in Italy the sows are generally kept living in groups during all or most of the pregnancy period, without getting particular problems of reproduction. In order to detect if grouped sows really develop high levels of aggression, we observed some of these during the second half of the pregnancy, recording in each observational session the aggressive interactions performed by every individual
