Nose rings are used in outdoor pigs to prevent rooting that damages pasture — but they frustrate one of the pig's most strongly motivated natural behaviours.
Nose ringing frustrates one of the most strongly motivated behaviours in pigs — rooting. Pigs with rings experience pain whenever they attempt to root, which they will repeatedly try to do because the motivation is so strong. This creates a chronic frustration cycle where motivation drives the attempt and pain inhibits the action. The welfare solution is not to add pain to prevent a natural behaviour but to manage rooting through pasture rotation, wallows, and providing dedicated rooting areas. Some outdoor producers have demonstrated that ring-free management is commercially viable with appropriate land management.