Social facilitation in the feeding behaviour of pigs and the effect of rank

Two groups each of three fattening pigs were used. After the rank order had been determined, the animals in each group were deprived of food for 12 hours. One was then left in the experimental room, given food ad libitum, and allowed to eat to satiation. Within 10 minutes of having stopped feeding, one of the others from its group was put in the adjacent stall and allowed to feed. In all cases, the apparently satiated pig started to feed when the newly-introduced pig started to feed. When used as the remaining pig, the dominant pig in each group fed for longer and ate more than the other-ranking pigs when a hungry pig was introduced into the next-door stall. In order to test whether the resumption of feeding was due to the cessation of isolation or due to the feeding behaviour of the introduced pig, a second experiment was performed. The same groups were used plus another group of three similar pigs. After 12 hours of food deprivation, two pigs were left in adjacent stalls and allowed to feed until satiated. The third member of their group was then introduced and allowed to feed in a stall facing the other two. In all cases the remaining pair fed for appreciable periods. These results confirm that social facilitation, as defined here, occurred in the feeding behaviour of these pigs.