Comparison of Fixed and Rising Displacement Rates of CO₂ for Euthanasia of Aged Rats

Area of Science:

• Veterinary Science
• Animal Welfare
• Toxicology

Background:

• Euthanasia is a critical procedure in animal research.
• Carbon dioxide (CO₂) is a common euthanasia agent, but its efficacy and welfare implications depend on administration method.
• Aged rats, often used in preclinical studies, may have unique physiological responses to euthanasia agents.

Purpose of the Study:

• To compare the effectiveness and welfare implications of different carbon dioxide (CO₂) gas displacement rates for euthanasia in aged rats.
• To determine if varying CO₂ flow rates impact the time to critical endpoints like dyspnea, ataxia, recumbency, and death.
• To assess cardiovascular and behavioral parameters during CO₂ euthanasia to evaluate animal well-being.

Main Methods:

• Aged rats (n=59) were euthanized using rising CO₂ concentrations with fixed (30%, 40%, 50%) or increasing (10-30%, 20-40%, 30-50%) flow rates.
• Cardiovascular telemetry devices recorded physiological parameters.
• Video analysis by a blinded observer assessed behavioral endpoints.
• Histopathological evaluation examined tissue effects.

Main Results:

• Higher CO₂ concentrations resulted in a significantly shorter time to loss of consciousness and death.
• No statistically significant differences were observed in the time to dyspnea across groups.
• Behavioral assessments and histopathology showed no significant differences between fixed and increasing CO₂ flow rates.
• Slower CO₂ displacement rates did not improve welfare indicators but prolonged the euthanasia process.

Conclusions:

• Faster CO₂ induction rates lead to more rapid euthanasia in aged rats.
• Slower CO₂ displacement rates do not offer discernible welfare benefits and unnecessarily extend the euthanasia procedure.
• Optimizing CO₂ flow rates is crucial for efficient and humane euthanasia in aged rat models.