Assessing animal welfare: different philosophies, different scientific approaches.

Attempts to improve animal welfare have commonly centered around three broad objectives: (1) to ensure good physical health and functioning of animals, (2) to minimize unpleasant "affective states" (pain, fear, etc.) and to allow animals normal pleasures, and (3) to allow animals to develop and live in ways that are natural for the species. Each of these objectives has given rise to scientific approaches for assessing animal welfare. An emphasis on health and functioning has led to assessment methods based on rates of disease, injury, mortality, and reproductive success. An emphasis on affective states has led to assessment methods based on indicators of pain, fear, distress, frustration and similar experiences. An emphasis on natural living has led to research on the natural behavior of animals and on the strength of animals' motivation to perform different elements of their behavior. All three approaches have yielded practical ways to improve animal welfare, and the three objectives are often correlated. However, under captive conditions, where the evolved adaptations of animals may not match the challenges of their current circumstances, the single-minded pursuit of any one criterion may lead to poor welfare as judged by the others. Furthermore, the three objectives arise from different philosophical views about what constitutes a good life-an area of disagreement that is deeply embedded in Western culture and that is not resolved by scientific research. If efforts to improve animal welfare are to achieve widespread acceptance, they need to strike a balance among the different animal welfare objectives.