Mice and rats are the most commonly used laboratory animals worldwide, yet receive less welfare consideration than larger mammals despite evidence of complex social and emotional lives.
Rats and mice in research laboratories frequently experience social isolation despite being highly social species. The absence of conspecifics causes chronic stress that affects immune function, brain development, and research outcomes. Carbon dioxide euthanasia — the standard method in many facilities — causes air hunger and distress before unconsciousness, representing a welfare concern at enormous scale. Research has shown that impoverished housing conditions alter rodent behavior and physiology in ways that compromise both welfare and the reproducibility of research results.