Non-nutritive chewing by pigs: implications for tail-biting and behavioral enrichment.

Groups of six juvenile pigs were presented with chewable materials (braided cotton cord or rubber strips). The time spent chewing the materials was quantified over 48 h by time-lapse video recording. A 150 mm length of braided cord attracted considerable chewing (average of 30 min/day/pig) and the behavior caused much fraying and damage to the exposed end of the cord. However, the pigs chewed very little (2 min/day) on the same material when it was presented as a loop with no exposed end. Solid rubber strips, which were much less easily destroyed, attracted only half as much chewing as the cord, but a straight length with an exposed end was still chewed much more (average of 12 min/day/pig) than a loop (1 min/day). The amount of chewing on a loop of cord increased dramatically when a small cut was made to allow the material to be damaged more easily. This suggests that easily damaged materials attract much more chewing than less destructible ones, but even with relatively indestructible materials, the presence of an exposed end increases the amount of chewing. The results have implications for understanding tail-biting outbreaks and for behavioral enrichment of pig environments.