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We have long recognized the impact that pain, stress, and distress can have on the welfare of laboratory animals, or for that matter, any animal. Pain and stress can cause distress, and the biologic effects can compromise experimental results (Moberg 1999). For these reasons, we are continually striving to control and ameliorate the effects of pain and stress on laboratory animals. Neither pain nor stress—a part of an animal's life, as they are ours— can ever be totally eliminated. Pain normally serves as a protective function to warn of impending danger and is therefore adaptive. Animals have evolved appropriate biologic strategies to assist them in coping with stress. Thus, pain and stress are not inherently bad for an animal, unless these biologic strategies fail to protect the animal from stress or the biologic cost of coping takes too great a toll on the animal. Then the animal experiences distress and its welfare is threatened. The question is, when does an animal cross over from nonthreatening stress to distress?
Carstens et al. (Sat,) studied this question.