Reactive abnormal behavior is the convincing proof of immaterial suffering for the ethologist. We consider abnormal that behavior which does not correspond to, or is without object, which appears with sharply increased or decreased frequency, or which is abnormal in its motor pattern. Moreover, much reactive abnormal behavior manifests itself in stereotypies, i.e., the movement is repeated continuously in the same way. Among wild animals and in traditional forms of animal production abnormal behavior is unknown. However, it is encountered often in animals in intensive husbandry systems, and it can be demonstrated that abnormal behavior is actually brought about by conditions of husbandry. It first appears when animals are transferred from good to poor conditions of husbandry. When the conditions are improved the abnormality declines. Often, however, it remains to some extent for a prolonged period even after conditions have been improved. Abnormal behavior is then characterized as residual-reactive. The obstinacy with which the abnormality remains is a further indication that the animal is highly neurotic.
Sambraus, H.H. (1981). Abnormal behavior as an indication of immaterial suffering. International Journal for the Study of Animal Problems, 2(5), 245-248.