Agonistic behaviour in grouped sows. I. The influence of feeding

Groups of sows were observed in cages with concrete floors from day 50 of pregnancy for 3 periods of a week each over the following 5 weeks. The aggressive interactions were noted during 4 observational sessions of one hour in every weekly period in situations unconnected with food or starting from food delivery. Interactions in connection with the use of the drinking nipples were scored separately during these periods. The frequency of agonistic interactions was much higher when the sows were competing for food, and also the behaviour pattems displayed varied in connection with the situation, i.e. the presence or absence of food in the pen. The highest incidence of aggression was noted within 30 minutes after food delivery, but, as a whole, the aggression declined during the one-hour session when the food was present. In the other context the aggressive level among the group was very low and the frequency of interactions remained stable. Almost all sows were involved in interactions when no food was present, while fewer (generally the dominant ones) when feeding. The latter displayed also behaviour patterns considered more aggressive. The results of this study indicate that aggression in grouped sows is not a problem and do not support the practice of tethering or keeping them in individual stalls in order to avoid the supposed danger of fighting among these animals.