Improvements in the welfare of animals arise from two primary sources: Changes in public attitudes and beliefs regarding what constitutes acceptable treatment of animals, and mandatory changes in behavior toward animals imposed by governments and regulatory authorities. During the last 30-40 years, public and political support for improvements in animal welfare has increased dramatically in many countries. Funding from both governmental and non-governmental sources continues to grow, and the relatively new field of animal welfare science has emerged and expanded to support and inform these efforts. Many experts in the field recognize, however, that there is still a distinct gap between the science and the practice of animal welfare, and that policies and actions that aim to protect animals from harm are sometimes implemented in the absence of reliable evidence that they actually work.
Serpell, James A., "On Measuring Progress in Animal Welfare" (2008). Assessment of Animal Welfare. 7.