quantification of the efficacy of analgesics in treating acute pain (Dixon et al. 2002 ,
2007 ). Studies of chronic pain have been focused on clinical conditions similar to
human situations of chronic or neuropathic pain; they are intended more to establish
the means of reducing the onset of severe pain than general alleviation of chronic
pain, associated with, for example, arthritic conditions.
However, several points of interest have derived from clinical behavioural
observations of cats in pain. First, cats frequently hide from their owners when
experiencing pain and this action obviously hinders the recognition of pain in this
species. Secondly, cats may still purr when in pain, contrary to the belief of many
owners that purring is invariably a sign of contentment. The more obvious signs, as
in dogs and most other species, include vocalisation, lameness, guarding of an area,
inappetance, reluctance to move and failure to groom. However, if the cat or dog
hides, then some or all of these responses are likely to be lost to the observer.
3.3 Horses and Other Equines
Much of the focus of pain studies in horses has been on two conditions, lameness
and colic. The reasons for this are that a lame horse is of limited use to its owner
both for draft purposes or for riding and horses with colic symptoms have relatively
high mortality rates. However, the range of painful conditions a horse may experi-
ence is essentially as wide as for any other species.
There have been many studies on the causes and localisation of lameness in
horses and there is a corresponding extensive literature which has established that
equine pain can be acute, chronic or intermittent, can range from mild to severe and
can have a variety of causes, including trauma, infection, allergic and genetic
factors. In addition, the anatomical source can range from the spinal column to
the foot and include all joints and tissues. Accurate diagnosis of the site of lameness
in horses has been described extensively, as have the available treatments. In many
cases a variety of remedies have been used, but far less focus has been made on the
treatment of the pain than on the likelihood of obtaining a cure and hence a sound,
and therefore saleable, horse.
There have, however, been many reports describing the treatment of pain in cases of
colic, as “colic” signifies “abdominal pain”. Several causes have been identified,
ranging from the unpleasant to the fatal. Some authorities have questioned the treat-
ment of colic pain, because of possible interference with making a correct diagnosis.
Consequently, a horse might recover from what had been diagnosed as a fatal form,
despite the fact that it is also possible that a horse might die from the stress of the pain
associated with some forms. However, it is now widely recognised that analgesic use
may allow a better clinical examination and hence facilitate the diagnosis.
Several studies on analgesic efficacy in the horse, using models such as abdominal
visceral distension (Pippi and Lumb 1979 ), tendon injury (Chambers et al. 1993 ),
induced arthritis (Morton et al. 2005 ), and local inflammation (Kamerling et al.
1985 ; Lees et al. 1987 ) have been published. The behavioural changes associated
Pain and Analgesia in Domestic Animals 171