Some farmers install nose rings on their pigs to inhibit a behavior known as rooting. When pigs root, they use their noses to burrow into the ground, turning it over to expose material of interest. While rooting is an entirely natural behavior, it can be very destructive, and pig rings are used to reduce the overall damage which can be caused by pigs. Not all farmers use pig rings, and there is some debate over their use.
Unlike cattle rings, which are inserted through a piercing made by a veterinarian, pig nose rings are usually simply clipped on. The ring makes it hard to root, because it gets in the way of the nose and causes pain if the pig persists in rubbing its nose in the soil. Eventually, the clip on ring may slide off, requiring replacement, and some farmers clip multiple rings onto the pig's nose to reduce the need to handle the pig for ring replacements.
When pigs are kept entirely indoors, the rings can be critical for protecting the health of the pigs, because they will become stressed and engage in rooting behavior, even if their pens are made entirely from concrete and other hard materials. A pig may scratch its nose up in the process of trying to engage in a natural behavior, raising the risk of potential infections in the pig. Nose rings can also reduce fighting among indoor pigs.
For pigs that are kept outdoors, rings prevent damage to pastures where the pigs range. Pigs are curious animals, and they tend to tear up confined pastures to express their boredom, and to look for items of nutritional value or interest. Using larger pastures and rotating pigs can reduce rooting damage, but nose rings may also become necessary. In areas where pigs are allowed to roam on public lands, a tradition known as pannage, rings may be required for loose pigs so that the animals do not damage common areas.
Some people argue that nose rings are inhumane, because they cause pain and suffering to the pigs. Inhibiting a natural behavior can create psychological problems, especially in pigs which are kept in close quarters, and the use of rings also prevents pigs from supplementing their diet with nutrition they find in the earth, which can be a major problem if pigs are not fed a balanced diet. Other people argue that the devices are sometimes a necessary part of pig husbandry, and that when installed competently, they should not cause undue distress.