A REVIEW OF BEHAVIORAL-FACTORS INVOLVED IN THE DEVELOPMENT AND CONTINUED PERFORMANCE OF STEREOTYPIC BEHAVIORS IN PIGS

Environmentally induced stereotypies, commonly observed in farm and zo o animals, are behaviors that are relatively invariant, that are regul arly repeated, and that serve no obvious function. However, there is a s yet no accepted means of discriminating between. normal and abnormal behavior, and the assumption that stereotypies are abnormal may mask the fact that they arise in part through processes that ''normally'' c ontrol behavior. There is growing evidence that stereotypies in sows a nd broiler breeders are strongly related to feeding motivation. For ex ample, sows only develop oral stereotypies if their feed intake is res tricted, and operant conditioning experiments have shown commercial le vels of feed restriction to give rise to high levels of feeding motiva tion. Stereotypies in animals whose feed intake is restricted largely occur in the postprandial period, and ingestion of food has specifical ly been shown to elicit stereotypies in sows. These observations sugge st that positive feedback from feeding produces a short-term increase in feeding motivation that at the end of the meal is directed toward a vailable, alternative stimuli such as chains, the choice of stimuli re flecting the sensory feedback from the activity. Drinking behavior may also become an expression of feeding behavior after metabolic water r equirements are met. In addition to these processes specific to feedin g motivation, it seems likely that nonspecific processes, which operat e more generally across motivational systems, contribute to the persis tence of the behavior. Behavioral arousal may facilitate performance o f active behaviors, and sensitization of the underlying neural element s may lead to the behavior being more easily elicited and maintained. A crucial factor in the sensitization process would seem to be the cha nneling of complex behavior by the environment into a few and very oft en repeated sequences of behavior. This approach suggests that stereot ypies can be prevented by either reducing the level of motivation unde rlying the stereotypy, or by allowing for the expression of more compl ex behavior and thereby preventing the processes of channeling and sen sitization from occurring.