Identifying individual laboratory animals is necessary for experimental tracking, but identification methods vary significantly in the pain and stress they cause, with important welfare implications for method choice.
Identification method choice accumulates welfare significance across the enormous numbers of animals used in laboratory research. Ear notching performed on thousands of mice in a single facility represents a large number of individual pain events that could be reduced by transitioning to less invasive alternatives. The welfare comparison between methods requires considering both the acute pain of the procedure and any ongoing welfare cost — ear notch wounds that become infected cause prolonged harm, while subcutaneous microchips, once healed, cause no ongoing welfare cost. Institutional culture often perpetuates established methods without welfare-based comparison of alternatives. The 3Rs principle of Refinement specifically includes improving identification methods as a welfare-relevant intervention. Facilities that have audited and transitioned their identification methods report equivalent experimental validity with reduced welfare cost.