Mice are by far the most used laboratory animal worldwide and significant welfare improvements come from providing environmental enrichment meeting their behavioral needs.
Mouse welfare in laboratory settings has improved substantially as the scientific case for enrichment has strengthened. Social housing, nesting material, and environmental complexity reduce corticosterone levels, stereotyped behavior, and aggression. These improvements also benefit research quality because stressed animals produce more variable and less reproducible results. The grimace scale has revolutionized pain assessment by providing an objective tool for detecting subtle pain states. Despite progress, millions of mice still live in barren conditions because enrichment is viewed as an operational burden rather than a scientific and ethical necessity.