Simple SummaryBans or restrictions on non-therapeutic tail docking of canine puppies are becoming more widespread. Justifications for constraining this practice have usually referred to hindrances to the tail contributing to unambiguous communication between different dogs, the marked acute pain presumed to be experienced during the docking procedure itself, the subsequent occurrence of chronic pain and heightened pain sensitivity, and other harmful complications. The present re-examination of these matters led to the following conclusions: first, the contribution the tail makes to canine communication has been seriously underestimated; second, the capacity of puppies to consciously experience any pain at the early ages docking is usually conducted has been markedly overestimated; third, the probability that docking causes significant chronic pain and an ongoing heightened pain sensitivity is reaffirmed as high; and fourth, other harmful effects are apparent, but their prevalence is not well documented. Nevertheless, it is concluded that, overall, the life-long negative welfare impacts of tail docking in puppies, especially impacts associated with impaired communication, as also the occurrence of chronic pain and heightened pain sensitivity, still strongly justify banning or restricting docking unless it is undertaken for therapeutic purposes.AbstractLaws, regulations and professional standards increasingly aim to ban or restrict non-therapeutic tail docking in canine puppies. These constraints have usually been justified by reference to loss of tail participation in communication between dogs, the acute pain presumed to be caused during docking itself, subsequent experiences of chronic pain and heightened pain sensitivity, and the occurrence of other complications. These areas are reconsidered here. First, a scientifically robust examination of the dynamic functional foundations, sensory components and key features of body language that are integral to canine communication shows that the role of the tail has been greatly underestimated. More specifically, it shows that tail behaviour is so embedded in canine communication that docking can markedly impede unambiguous interactions between different dogs and between dogs and people. These interactions include the expression of wide ranges of both negative and positive emotions, moods and intentions that are of daily significance for dog welfare. Moreover, all docked dogs may experience these impediments throughout their lives, which challenges assertions by opponents to such bans or restrictions that the tail is a dispensable appendage. Second, and in contrast, a re-examination of the sensory capacities of canine puppies reveals that they cannot consciously experience acute or chronic pain during at least the first week after birth, which is when they are usually docked. The contrary view is based on questionable between-species extrapolation of information about pain from neurologically mature newborns such as calves, lambs, piglets and human infants, which certai...