Mice and rats are highly social animals whose welfare in research settings is significantly impaired by individual housing, and the scientific evidence increasingly supports social housing as both an ethical and methodologically superior approach.
The individual housing of laboratory rodents represents one of the largest-scale welfare problems in animal research, affecting tens of millions of mice and rats annually. These are social animals for whom isolation is a form of chronic stress — not a neutral state. The scientific justification for individual housing is often overstated: the majority of research endpoints are not meaningfully affected by whether mice are housed alone or with conspecifics, and stressed animals from impoverished environments may actually produce less reproducible data. The welfare case for social housing is clear; the scientific case is also strong. Implementing social housing as the default — with individual housing requiring scientific justification — would be a major welfare improvement for one of the most numerous categories of animals used in research.