To understand why potbellied pigs become aggressive, we need to understand their herd instincts. In the wild, pigs travel in herds. Wihin this herd structure, there is a very defined heirarchy, similar to a pecking order in chickens. When two pigs meet for the first time, they fight — often viciously. This fighting may include posturing and frothing at the mouth; the hair on the back of the neck may stand up and the tail may point straight out and wag. A fighting pig will position him or herself so that his head aligns with the other pig’s shoulder. The pigs will slam their heads into each other’s shoulders, cutting with their tusks and wiping the foam from their mouths onto the other pig. This foam contains the pig’s scent, and marks the other pig with the smell. The fighting will continue until one pig admits defeat and runs away. A pig fight to establish dominance in the herd heirarchy can take hours.
Pigs appear to have very little concept of size. An adult pig will fight with a piglet a tenth his size, or with a farm pig ten times his size. Smaller pigs are frequently more agile and it can be difficult for larger pigs to catch them.
We have also observed behaviors such as tail biting, leg biting and ear biting. Although we know of only one pig who has ever lost a tail during a fight, it is common for major damage to occur to the ears. During a fight, pigs’ ears can be split in two or a portion may be completely ripped off. When this type of injury occurs, the hurt pig will immediately submit to the dominant pig and search out mud with which to coat his injury. By covering the injury in mud, the pig prevents insects from accessing the wound.