Welfare measurement has evolved from simple input-based assessments (how much space?) to sophisticated outcome-based indicators that assess the actual experience of individual animals.
Measuring welfare accurately is a prerequisite for improving it. Input-based measures — number of animals per square meter — can be gamed and miss actual experience. Animal-based outcomes — lameness scoring, lesion prevalence, fear response — tell us about the life the animal is actually having. The science of welfare measurement enables evidence-based policy and management.