with these models have also been described. Gait analysis in horses has dated from
the earliest days of cinematography. However, the development of force plates and
platforms has allowed a much more advanced, computer-based, analysis of both the
forces and movements associated with lameness in horses (Barr et al. 1995 ). This,
in turn, has facilitated studies of the efficacy of analgesic agents in many forms of
lameness (Symonds et al. 2006 ). Horses are another species in which electroence-
phalograms have been used to evaluate pain and analgesic actions (Ekstrom et al.
1993 ; Murrell and Johnson 2006 ).
In summary, there is a strong clinical impression that horses are very sensitive to
pain and they show extreme distress on exposure to noxious stimuli. However, in
many countries the apparently limited distress exhibited by donkeys and mules has
led to both their popularity and ill-treatment and the frequent lack of treatment of
painful conditions in these animals is a cause for serious concern for all persons
concerned with animal welfare.
3.4 Cattle, Sheep, Goats and Camels
Ruminant species in general seem to be rather non-demonstrative to pain when they
are examined superficially. However, when observed by an experienced person a
variety of subtle responses are apparent. This supports the supposition referred to in
Sect. 2.2, whereby these herd animals, in not showing overt abnormal behaviour,
may avoid the attention of would-be predators that seek out an animal which shows
some sign of “weakness”. Thus, the lack of overt pain behaviour becomes a survival
strategy and allows the animal to blend in with the rest of the herd.
Probably the most commonly observed pain in ruminants relates to lameness,
which may be acute or chronic in nature. As in horses, the range of predisposing
factors can be very wide, but they are frequently a manifestation of pain. In the case
of dairy animals, one of the responses to pain is a reduction in milk production and
consequently, these factors have received significant attention, focusing mainly on
prevention rather than treatment of pain, because the potential problem of analgesic
drug residues in milk has restricted their use (Espejo et al. 2006 ). However, there is
a significant literature on the use of analgesics in ruminants, although there are still
concerns over the accurate diagnosis of pain, particularly in cases of chronic or
intermittent pain. More recently, the assessment of chronic lameness in dairy cattle
has been addressed using computerised gait analysis and these studies can also be
used to evaluate treatments (Flower et al. 2005 ).
In other ruminant species only the sheep has received significant attention in
terms of pain assessment and alleviation and pain-related behaviours. This is partly
due to the availability of sheep as a more easily housed and handled model for pain
in cattle. Moreover, the sheep is a compliant species for pain and analgesia studies
(Nolan et al.1987a). Sheep have also been used to provide a model for chronic pain,
due to the frequently occurring disease “footrot”, which has enabled studies to
be undertaken on the development of chronic pain in this species (Ley et al. 1989 ).
172 A. Livingston