psychological well-being are due to a lack of direct reporting of the state of well-being by the subject (no language), not knowing what minor changes in well-being really mean to the animal, and not knowing what the impact is of levels of well-being on the research (which probably varies with the study).
There are advantages to using animal behavior as an assessment tool. For example, behavioral assessment is probably the least intrusive measure; and in the hands of a skilled, knowledgeable observer, behavior as an indicator of well-being (or lack thereof) can be reliable and powerful. A knowledgeable observer has the expertise to use different criteria in different species and to gauge their significance, and the skilled observer will predicate his/her assessment on the animal 's milieu, including its physical environment, the research it is used in, and the animal's own status (e.g., its age and health).
However, there are also some disadvantages to using animal behavior as the assessment tool. Early experience (which may not be known), age, and physiological state can influence the behavioral response of an animal leading to interand intra-animal variability. For example, some research indicates that young animals are more responsive to pain stimuli than older animals and that sick animals may also be more responsive than healthy counterparts.
As has often been noted, correlations of specific pain-related behavior with intensity of the pain experience cannot be made. There is no behavior expressed by animals that indicates the severity of pain being experienced. Even the assessment of the efficacy of an analgesic is based on rather crude analgesiometric tests such as a hot plate or tail flick test.
There are too many amateur behaviorists, which can lead to overconfidence in their abilities. One lecture or even one course in animal behavior does not turn someone into an expert, just as the college courses I took in accounting and economics did not turn me into an Alan Greenspan. Our exposure to animal behavior through the popular press and television lulls us into a belief that we all have knowledge in the field and skills in understanding animal behavior.
When evaluation criteria for pain are sought, a common approach is the use of general behavior that is extrapolated into indicators of pain in several species of laboratory animals. The problem is that this approach is rife with subjective criteria and/or contradictions. For example, Morton and Griffiths' (1985) seminal article, “Guidelines on the Recognition of Pain, Distress and Discomfort in Experimental Animals and an Hypothesis for Assessment,” which has influenced numerous working group reports and reviews over the years, includes a table of specific, summarized behavioral signs indicative of pain and distress. Categories of behavioral criteria used by the authors are posture, vocalizations, temperament, locomotion, and other. Several of the behavioral criteria, such as dormouse