Some breeds of domestic pigs have curly tails, and different theories as to why exists. One theory states that ancient Chinese farmers liked the select for it, because the curly-tail trait was linked to a strong trait that Chinese farmers preferred, according to Life 123. Another theory suggests that the curly tail reduces tail injuries in domestic pigs kept on farms, states Life 123.
Wild pigs and many breeds of domestic pigs do not have curly tails. In wild pigs, the straight tail is used for communication with other pigs. The curly-tail trait may been accidentally carried along with other dominate traits during early pig breeding, according to U.S. Department of Energy, Newton Ask a Scientist.
The theory that curly tails were selected for, in order to reduce tail injury in domestic pigs, is possible but unproven. Many factory-farms, that include confinement feeding operations, dock the tails of piglets and clip their teeth in order to prevent injuries, says The Independent. However, the tail injuries seen in modern factory farms seem to be created by the conditions the pigs are kept in. Pigs kept under more natural conditions do not bite each others' tails, according to Natural Pig Farming. It is unlikely that the Chinese farms, where the curly-tail trait originated, kept pigs in factory-farm type conditions.