Mice and rats are the most commonly used laboratory animals, and their welfare is shaped by housing conditions, procedures, and institutional culture.
Laboratory rodents in inadequate housing suffer from social isolation, environmental barrenness, and unpredictable handling. Group housing with nesting material and hiding places dramatically improves welfare indicators. Tail suspension and other restraint methods cause acute stress. Analgesic use after painful procedures is improving but inconsistent. The sheer scale of rodent use in research means small improvements in individual welfare multiply to enormous aggregate benefits. Institutional culture and leadership are the primary drivers of welfare quality.