Euthanasia is a major welfare concern for laboratory animals, as the method used profoundly affects the quality of death. Better standards reduce suffering at the end of animal lives in research.
Euthanasia is paradoxically one of the most welfare-critical moments in a laboratory animal life, yet it often receives less attention than procedures performed during the animal use. The common use of carbon dioxide for rodent euthanasia is a significant welfare concern: rodents actively avoid CO2 atmospheres, show distress behaviors during exposure, and may experience an aversive period of consciousness before losing awareness. Less aversive methods exist and are increasingly recommended, but adoption is slow due to cost, convenience, and institutional inertia. Ensuring that the end of a laboratory animal life is as free of suffering as possible is both an ethical obligation and a practical expression of the respect for animal life that should characterize responsible research.