The less commonly used routes of drug administration such as intra-articular or
epidural routes are nevertheless used routinely for analgesic drug administration in
most domestic species. Moreover, the concept of multidrug administration to
achieve “balanced analgesia”, particularly in association with post surgical pain
control, is now widely practised (Dobromylskyj et al. 2000 ).
A further strategy worthy of mention is the use of acupuncture. This is widely
used in human medicine as a means of controlling pain, with increasing acceptance
alongside traditional “Western” medicine approaches. The same applies to veteri-
nary medicine. There has been general acceptance of the procedure and several
studies have been published on the relevant points and meridians for some animal
species, which do incidentally differ from those used in humans (Gaynor 2000 ).
Most reported studies in animals have used needle acupuncture, although some
other modalities have been reported (Gaynor 2000 ; Mittleman and Gaynor 2000 ).
The evaluation of acupuncture on pain in animals has been dogged by the same
problems as controlled studies in humans, namely the difficulty in ensuring accept-
able controls in the form of a credible placebo, although there have been many
claims based on behavioural responses, particularly in chronic pain control (Wright
and McGrath 1981 ; Martin and Klide 1987 ; Klide and Martin 1989 ). There are also
a number of other strategies that have been adopted from human practise and used
with the intention of controlling animal pain. These include chiropractic and herbal
therapies, as well as more esoteric therapies and more mainline ones such as
massage and exercise therapies (Manning et al. 1997 ; Millis and Levine 1997 ). In
some instances, the efficacy of these approaches remains to be established.
2.5 Pain Perception in Animals
The pain modality easiest to recognise and treat in domestic animals is acute pain.
Like humans, this is associated in many cases with some form of trauma, either
accidental or surgical, and is often clearly associated with some specific body
region. In addition, the onset of acute pain can be associated with some infectious
diseases, and acute inflammation in states such as pneumonia, peritonitis or cystitis
may be the presenting sign. Clearly, diagnosis of the cause of acute pain is of great
importance and in animals this issue is exacerbated by the lack of verbal communi-
cation. It is of interest to note that the development and extent of analgesic drug use
in humans has been based to a large extent on acute responses to pain by animals.
Early evaluations were performed using a murine model, based on its response to a
heated hot plate of foot lifting and licking (Woolfe and McDonald 1944 ) or on the
time taken by rats to remove their tail from hot water (D’Amour and Smith 1941 ).
In addition, there was a commonly used test in the rat involving removal of a
forepaw from a gradually increasing pressure on the footpad (Randall and Selitto
1957 ). These early tests comprised behavioural responses to an acute painful
stimulus and they are sufficiently consistent and validated to provide the prelimi-
nary evaluation of analgesics developed for humans. It might be noted that all these
Pain and Analgesia in Domestic Animals 165