undesirable and unnecessary in humans, it was inevitable that, eventually, the
concept of alleviation of pain in animals would follow.
However, this concept has been hard to implement in many cases, often asso-
ciated with the variability in response to pain in various species of animals. Of all
the animal species, humans are among the most demonstrative in their response to
pain. They vocalise strongly, they show profound escape behaviour and they enlist
the help of their peers in attempting to prevent or alleviate their pain. The group of
animals which most closely parallels these responses is, not surprisingly, monkeys.
However, many species show much less overt reactions to painful stimuli. This is
particularly apparent in animals which live in large groups and are often subjected
to predation, such as wildebeest and zebras in the wild and cattle and sheep in
domesticated groups (Livingston 1994 ). There seems to be a survival strategy
adopted by these species, in that predators in the wild become focussed on indivi-
duals of the prey species who show some abnormal behaviour. Thus, if a prey
animal is showing overt signs of pain then its chances of avoiding a predator are
much diminished, so the lack of overt behaviour may become a survival strategy;
this is the opposite of a human who wishes to gain the support of their social group
to survive. This has led to the conclusion that, if an animal does not overtly
demonstrate pain then it is not feeling pain, which is clearly an error. These
concepts have led to an unacceptable reluctance to treat painful situations in
domestic cattle, sheep and similar species as well as non-mammalian species, all
of which are non-demonstrative in behaviour and vocalisation. The level of under-
standing of pain in humans has progressed significantly over the past few decades,
both in our knowledge of the mechanisms involved and in effective treatment
strategies. Fortunately, similar advances are being made for animals as well,
especially in the more difficult areas such as neuropathic pain.
2.3 Analgesic Factors
Advances in our understanding of animal pain have led to the development of
strategies for assessing this pain, based on behavioural responses for several
species, the difficulty being however that the behavioural indicators do not readily
apply to species other than the one they were developed for. An additional factor is
that the behavioural indicators that apply to acute pain do not necessarily apply to
chronic or neuropathic pain. Consequently, multiple evaluations are required to
adequately describe the multiple species and several pain entities that they may
suffer from. Moreover, there is a need to take into account the concept of individual
variation within a species in pain response, which has been well documented in
relation to genetics (Critchley et al. 1986 ; Mogil 2004 ), gender (Walker and
Carmody 1986 ) and age (Gibson and Weiner 2005 ). The best behavioural indicators
that have been developed for animals consist of VAS, which take into account a
variety of behaviours and circumstances and these, taken together, provide an
estimation of the intensity and duration, and possibly the nature, of the pain from
Pain and Analgesia in Domestic Animals 163