response to stressful stimuli has been shown to be subject to the early experience of the animal (Melzack and Scott, 1957; Green, 1978). Adaptation and handling to minimize stress and prevent distress can be applied to many experimental settings and procedures: chair restraining of nonhuman primates (when necessary for short periods) should be preceded by a series of brief introductions to the chair by a familiar person and rewarded by favorite foods either in the chair or immediately on returning to the home cage. Movement of animals to test chambers or laboratories should be preceded by several days or weeks of conditioning trips in which no aversive interaction takes place and food reward is provided. Through such means, a "transfer cage" or leash can signal a pleasurable event for the animal and facilitate a difficult task for the responsible person. In each case, the goal should be the positive association of the desired task favorably with a conditioned stimulus, such as the transfer cage, leash, or familiar technician. The stimulus need not always be a physical entity; the time of day or the ring of a bell can come to convey the same information, if presented in a predictable and routine manner and associated with the event to which the animal is being adapted. Adaptation to strange or unusual objects or environments, before the experimental introduction of the animal to the object or environment, reduces the novelty and stress of the experience and the likelihood that it will affect the experimental results.
Other experimental procedures and poor or inappropriate techniques, such as those common in blood withdrawal or antibody production, also can lead to stress. Amyx (1987) summarized procedures for antibody production, emphasizing that a reduction in volumes injected and a change in the site of injection minimizes the pain and distress of immunization procedures. Distress can be further minimized by sedative pretreatment, rather than use of restrainers. Blood withdrawal can lead to stress if the amount removed exceeds 1% of the animal's body weight.
Adaptation and socialization are strategies for reducing the distress of laboratory animals, preventing or alleviating distress, and thereby enhancing their well-being.