Purpose
Historically, tail docking was thought to prevent rabies, strengthen the back, increase the animal's speed, and prevent injuries when ratting, fighting, and baiting. In early Georgian times[clarification needed] in the United Kingdom a tax was levied upon working dogs with tails so many types of dogs were docked to avoid this tax.
The tax was repealed in 1796 but that did not stop the practice from persisting.
Tail docking is done in modern times either for prophylactic, therapeutic, or cosmetic purposes. For dogs that worked in the field, such as some hunting dogs and herding dogs, tails could collect burrs and foxtails, causing pain and infection and, due to the tail's wagging, may be subject to abrasion or other injury while moving through dense brush or thickets.
Modern practice
Docking to puppies fewer than 10 to 14 days old is routinely carried out by both breeders and veterinarians without anesthesia. Opponents of these procedures state that most tail dockings are done for aesthetic reasons rather than health concerns and are unnecessarily painful for the dog. They point out that even non-working show or pet dogs are routinely docked. As a result, tail defects that docking proponents claim makes docking necessary in the first place are perpetuated in the breeds.[clarification needed] They point to the many breeds of working dogs with long tails that are not traditionally docked, including English Pointers, Setters, Herding dogs, and Foxhounds.
Criticism
Robert Wansborough argued in a 1996 paper that docking tails puts dogs at a disadvantage in several ways. First, dogs use their tails to communicate with other dogs (and with people); a dog without a tail might be significantly handicapped in conveying fear, caution, aggression, playfulness, and so on.
Certain breeds use their tails as rudders when swimming, and possibly for balance when running, so active dogs with docked tails might be at a disadvantage compared to their tailed peers. In 2007, Stephen Leaver, a graduate student at the University of Victoria, published a paper on tail docking which found that tail length was important in the transmission of social cues. The study found that dogs with shorter tails (docked tails) would be approached with caution, as if the approaching dog was unsure of the emotional state of the docked dog. The study goes on to suggest that dogs with docked tails may grow up to be more aggressive. The reasoning postulated by Tom Reimchen, UVic Biologist and supervisor of the study, was that dogs who grew up without being able to efficiently transmit social cues would grow up to be more anti-social and thus more aggressive.
Wansborough also investigated seven years of records from an urban veterinary practice to demonstrate that undocked tails result in less harm than docked tails.