There should seldom be a question about the possibility that a laboratory animal is in pain, if basic principles are followed. U.S. Government Principles for Utilization and Care of Vertebrate Animals Used in Testing, Research, and Training (IRAC, 1985) states that "unless the contrary is established, investigators should consider that procedures that cause pain or distress in human beings may cause pain or distress in other animals." Experimentally induced pain is ordinarily predictable and either avoidable or relievable, according to the requirements of the research protocol. But unforeseen circumstances might place an animal in unexpected pain, and there must be ways to recognize it.
In evaluating procedures that cause pain and distress, one should justify the procedures and their potential benefits to humans or animals. Societal concerns about the welfare of animals used for experimental purposes necessitate that standards be developed to take into account all relevant information, including scientific data and observations from both biologic and behavioral sources. Guidelines should be established that ensure relief from pain or distress in any study (Dubner, 1987; Montgomery, 1987). Pain, stress, and distress that are not produced specifically for study should be viewed as unnecessary, unwanted, data-compromising side effects (Amyx, 1987; Spinelli and Markowitz, 1987). It must be emphasized that stress can still affect experimental results even if an animal under stress seems to be adapting and is manifesting no maladaptive behavioral or physiologic signs.
One of the more important responsibilities in the use of animals for biomedical research is to recognize clinical signs associated with pain. Without a knowledge of their normal and abnormal behavior and appearance, assessment of pain in animals is difficult, because animals are unable to communicate in ways in which they can be readily understood by people (Hughes and Lang, 1983; Soma, 1987).
An important step in determining that an animal is in pain is the recognition of a departure from the animal's normal behavior and appearance (Morton and Griffiths, 1985; Dubner, 1987; Kitchen et al., 1987; Dresser, 1988). Well-being is usually associated with species-typical behavior and is used as a descriptor for healthy animals that are adapted to their environment (however, see Chapter 3). A well animal will play with its cagemate or handler, exhibit normal curiosity through explorations, keep itself well groomed, appear to be in good health, grow normally, and have normal reproduction.
There are no generally accepted objective criteria for assessing the degree of pain that an animal is experiencing (Morton and Griffiths, 1985), and species vary widely in their response to pain. However, some behavioral signs are usually associated with pain (Table 4-1). Animals often communicate pain by their posture.