Effects of predictability on the welfare of captive animals

Variations in the predictability of a stressor have pronounced effects on the behavioural and physiological effects of stress in rats. It is reasonable to expect that variations in the predictability of husbandry routines thought to be aversive to animals might have similar effects on stress indices. Similarly, variations in the predictability of positive events, of which feeding is an obvious example, may affect welfare. This review examines the behavioural and physiological effects of the predictability of aversive and appetitive stimuli, and the application of experimental findings to animal husbandry in practice. It is argued here that two distinct but overlapping types of predictability exist. ‘Temporal’ predictability describes whether an event occurs at fixed or variable intervals, whereas ‘signalled’ predictability relates to the reliability of a signal preceding the event. This review examines the effects of each of these types of predictability in relation to positively and negatively perceived events, and examines the link between predictability and control. Recommendations are made for relatively simple and inexpensive modifications to husbandry routines that may be easy to incorporate into the schedules of busy staff yet could have a profound impact on the welfare of animals in their care. # 2006 Elsevier B.V. All rights reserved.