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II. Pain and Distress: Recognition and Assessment

Many experts say too little is done for animals in pain since too little is known about how to judge their pain objectively. Lab workers rely on relatively insensitive measures, such as weight loss of 20% or more, as a sign that animals might be experiencing pain and distress1.

A more objective approach is to look at blood samples for elevations in glucose, corticosteroid, and catecholamine concentrations. Of course, these markers of stress require invasive procedures that of themselves can cause what they indicate.

Another strategy can demonstrate that pain exists in animals who cannot tell us directly of their pain. Experiments demonstrate that animals will readily learn to self-administer an analgesic. That they do so can be used as evidence that they are experiencing pain. For instance, in a set of investigations, rats drank a liquid containing analgesic medication that, if anything, tasted bad, choosing it over a sweet tasting solution-presumably because it alleviated their pain3.

Researchers are beginning to find better means to determine an animal's pain and distress objectively4. Only a decade or two ago, clinicians maintained that newborn human infants do not feel pain, and pain was not treated in neonates even after surgery. Revision of this attitude came about with a standardized scoring of facial expression and body posturing, which now is accepted as indicating pain in a newborn child.

Animals, like human infants, cannot speak to us about their pain. They do exhibit behaviors typical for their species, however. Minimally, observations that register if an animal has pain include: altered appearance of the hair from loss of grooming; licking, biting, scratching or shaking of a painful area; sweating or salivation; changes in personality or attitude or activity level; vocalization.

More careful observation can translate for each species the language of their behaviors to tell us if pain is being experienced. For instance, ear flicks in calves correspond to pain from dehorning. Back arching in rats corresponds to pain from surgery. High pitched squeals, accompanying the normal sounds of squealing in piglets, correspond to pain from castration. None of these behaviors is obviously tied to registering pain; close observation and analysis, however, reveals a connection6.

Indeed, it is the scientists who work with animals in research who are in the best position to define the ethology of pain and distress, either themselves, or by enlisting collaboration with those who study animal behavior. By taking the time to do so, researchers-and farm workers as well-can make systematic observations that may reveal ways to modify techniques to diminish animals' pain and distress.

An important aspect to determining pain by species specific behavior is to recognize that the need to avoid a predator overrides the expression of pain for so many species. Animals in pain must hide that fact to avoid looking like an easy lunch. The social nature of a species also influences its typical pain behaviors. This can explain why cows are stoic, and cats excited, in reaction to pain.

Temple Grandin, who has carried out extensive observation and formal research into the nature of pain in animals, relates: "We observed this behavior recently in a bull that was being castrated with a large rubber band. When he was unaware of being watched, he laid (sic) on his side and was moaning. As soon as he saw us, he jumped up and behaved as if he was not in pain until we left"8.

Scoring systems to assess pain are being devised for many species, including dogs, cats, horses, sheep, calves, and small rodents. Scoring is based on the degree to which an animal's physiology and mental state have deviated from normal9. This approach can extend to other vertebrates, and even non-vertebrates, providing there is a good knowledge of their normal behavior and physiology.

Regardless of the signs demonstrated, if there is any doubt that an animal may be experiencing pain, regulations call for a trial treatment with analgesics11.

NEXT: Alleviation and prevention of pain in animals


Readings and Resources on Recognition and Assessment of Pain and Distress

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