A dynamic approach to the study of environmental enrichment and animal welfare

Abstract

We agree with Mike Appleby that “variability in response has implications for environmental design and animal welfare, because it is often impossible to make definitive decisions on the values of specific features of the environment which are to be provided’ ’ . We suggest that a primary difficulty in deciding on appropriate environmental design is not the occurrence of animal responses to supernormal stimuli but the existence of environmental complexity that presents animals with many conflicting choices. We propose a dynamic approach to the study of environmental enrichment and animal welfare that recognizes the existence of trade-offs between these choices. The optimal outcome of these trade-offs will be the outcome that maximizes animal welfare. We recognize that there is no ideal currency for assessing animal welfare although fitness (reproductive success), or correlates of fitness such as energetic balance or other indicators of physical condition, may be useful starting points. Many advances in the understanding of behavioural ecology have been made using stochastic dynamic modelling despite imperfect information about reproductive success (Mange1 and Clark, 1988). We are, therefore, optimistic about the use of this approach in the study of animal welfare and environmental design. We do not deny that it is possible to design stimuli that are supernormal, evoking a stronger response than does the natural stimulus (Tinbergen, 1951). However, the concept of supernormality implies that the stimuli are rarely encountered, contrary to the situation in animal housing where animals continually or frequently encounter the features of their housing environment. Supernormality also implies that the animal’s response is innate and unmodified by learning. Furthermore, there is the problem of deciding what is “natural” for animals kept under a range of different housing conditions (Newberry, 1995). If responses to supernormal stimuli were detrimental to