The Refinement pillar of the 3Rs focuses on improving the lives of animals used in research. Advances in laboratory animal housing have significantly reduced suffering within existing research frameworks.
A mouse in a bare plastic box with no nesting material is a mouse in chronic stress. Providing nesting material costs pennies and dramatically improves welfare indicators including corticosterone levels, wound healing, and reproductive success. Refinement does not require replacement — it requires recognizing that stressed animals are also worse experimental models.