treatment of chronic pain in animals is associated with ethical debates (Mendl et al.
2001 ) regarding the cost/benefit situation for both the animal and the owner
(Gingerich and Strobel 2003 ).
Recently there has been increased interest in the occurrence of chronic post-
surgical pain in humans (Kehlet et al. 2006 ). In particular, the incidence of ongoing
post-surgical pain following a number of surgical interventions has received atten-
tion. While the existence of phantom limb pain following amputation has been long
recognised, it now appears that chronic pain following a number of orthopaedic,
abdominal and thoracic surgeries in man is much more frequent than was once
thought, and therefore significant under-reporting was probably present. The veter-
inary relevance of this phenomenon should be considered as most human pain
syndromes have been documented in animals. The routine ovario-hysterectomies
performed on dogs and procedures such as caesarean section on farm animals, as
well as surgical amputations of tails in dogs and other species for the convenience
or gratification of the owner, must have the potential for some degree of post-
surgical pain, although it may be that the increasing use of pre-emptive analgesia in
association with surgery has had some impact on the incidence of this entity.
Another more recent human pain concept which has been described, and which
may be related to post-surgical pain experience, is that of neuropathic pain. This is
broadly defined as the existence of pain without obvious pathology, and at one time
was regarded in some cases as a psychological phenomenon rather than the actual
pain entity now recognised. As it was often misdiagnosed in humans in the past, its
veterinary diagnosis in the absence of verbal communication or pathology presents
particular challenges. There are indications from some clinical case reports that
dogs can experience phantom limb pain on the basis of the observed stump mutila-
tion by chewing. As dogs and cats are the only species that are commonly subject to
therapeutic amputations, information in other species is limited. With regard to the
other neuropathies there are less data available, with the possible exception of
diabetic neuropathy which has been studied in companion animals (Mizisin et al.
2007 ). There are many other human conditions assessed as neuropathies with
associated pain such as pancreatitis (Winston et al. 2005 ), but the specific diagnosis
of neuropathy associated with these conditions in animals has not been reported.
3 Recognition of Animal Pain
3.1 Laboratory Animals
The most widely reported studies on the recognition of animal pain are those
conducted in laboratory animals, based on tests for analgesic drugs undergoing
development for human use. However, there are reports in the literature of pain
control strategies for laboratory animals focused on the welfare aspects of their use
(Liles and Flecknell 1992 ). This is also a relevant source of information for species
such as guinea pigs, rabbits, rats, ferrets and mice, which are kept as pets. Recent
Pain and Analgesia in Domestic Animals 167