When is CO2 euthanasia considered acceptable for mice, and what are important preconditions?

• A. Always; no preconditions required.
• B. When performed without proper ventilation or oversight.
• C. When performed with a validated flow rate and chamber, following IACUC guidance; ensure humane death and consider alternatives if needed.
• D. Only for mice over 5 kg; not relevant.

Answer: (C)

CO2 euthanasia is acceptable only when it is done with a validated delivery system and chamber, under IACUC-approved guidance, to ensure the death is humane and any distress is minimized. Using a validated flow rate and chamber means the equipment and protocol have been tested to reliably render the animal unconscious before significant suffering occurs, and the exposure is controlled to avoid unnecessary stress. Following IACUC guidance brings formal oversight, trained personnel, and review of the protocol, including consideration of alternatives if CO2 is not the best option for a particular animal or situation. Proper setup, monitoring, and the option to choose other methods when appropriate are essential to upholding welfare standards.