Laboratory rats are highly social animals that suffer significantly in isolation. Evidence-based housing improvements including pair and group housing dramatically improve rat welfare in research settings.
Social isolation causes genuine psychological harm to rats. Animals kept alone show depression-like behavioral states and physiological stress markers. Most research protocols can be conducted with socially housed animals when researchers are willing to adapt their designs. Providing nesting material alone represents one of the lowest-cost, highest-impact welfare improvements available in laboratory rodent facilities.