Rats are the most widely used mammal in biomedical research, and their high cognitive capacity makes environmental enrichment a critical welfare requirement.
The cognitive and social complexity of rats makes their welfare in research settings particularly important — and particularly consequential. Stressed rats show altered immune function, hormone profiles, and behavior that can confound research results, meaning poor welfare is both an ethical failure and a scientific problem. Minimum standards for rat housing have historically been inadequate for a species that lives in complex social groups and explores large home ranges. Progressive refinement programs include group housing where compatible, nesting and burrowing materials, environmental complexity, and handling protocols that reduce fear. These improvements benefit both animal welfare and research reproducibility.