Euthanasia Methods and Induction Techniques in Laboratory Rodents

Effective and humane euthanasia of laboratory rodents encompasses chemical, physical and emerging approaches, each governed by welfare imperatives and regulatory frameworks. Chemical methods include inhalant agents such as carbon dioxide (CO₂) and halogenated anaesthetics (isoflurane, sevoflurane), along with injectable barbiturates administered intravenously or intraperitoneally. Physical methods, sanctioned under specific guidelines, range from cervical dislocation and decapitation to blunt force trauma. Recent advances have explored refinements to minimise distress, including gradual decompression (hypobaric hypoxia), adjunctive gas combinations (for example nitrous oxide with CO₂) and optimised dosing regimens for injectable agents to ensure rapid loss of consciousness. Across all techniques, assessment of transitional states—loss of righting reflex, changes in heart rate, behavioural aversion—and attention to operator training and consistency are critical to safeguarding rodent welfare and ensuring reproducible scientific outcomes.

Research from Nature Portfolio

Survey data from UK laboratory animal personnel reveal a strong institutional reliance on four principal methods—CO₂ overdose, anaesthetic overdose, cervical dislocation and concussion—with notable variation in availability and operator preference. Although over half of respondents favour cervical dislocation, recommended flow rates for CO₂ are often poorly understood, and comprehensive, standardised training is lacking. These findings underscore the need for quality-controlled education programmes and continuous legislative review to align practice with welfare benchmarks.

Investigations into sodium pentobarbital overdoses during exsanguination demonstrate that high barbiturate doses, while ensuring irreversible unconsciousness, may perturb molecular and biochemical markers in harvested tissues. Elevated hypoxia-inducible factor and inflammatory transcripts, together with altered serum enzyme activities and oxidative-stress indicators, suggest that excessive anaesthetic exposure can confound downstream analyses. These results advocate for carefully titrated dosing regimens to balance rapid euthanasia with preservation of tissue integrity.

Euthanasia Methods and Induction Techniques in Laboratory Rodents publication trend

The graph below shows the total number of articles in euthanasia methods and induction techniques in laboratory rodents across all publications each year (not limited to Nature Index journals).

Technical terms

Carbon dioxide euthanasia: Method in which animals are rendered unconscious and killed by inhaling CO₂ gas at controlled flow rates.

Hypobaric hypoxia: Euthanasia technique using gradual decompression to induce low oxygen partial pressure, leading to unconsciousness.

Loss of righting reflex (LORR): Absence of an animal’s ability to correct its posture when placed on its back, used as an indicator of loss of consciousness.

Intraperitoneal injection (IP): Administration of agents into the peritoneal cavity, commonly used for barbiturate euthanasia.

Exsanguination: Removal of blood, often combined with anaesthetic overdose to ensure death and facilitate tissue collection.

References

1. The perspectives of UK personnel towards current killing practices for laboratory rodents. Scientific Reports (2023).
2. Striving for humane deaths for laboratory mice: hypobaric hypoxia provides a potential alternative to carbon dioxide exposure. Proceedings of the Royal Society B (2023).
3. Sodium pentobarbital dosages for exsanguination affect biochemical, molecular and histological measurements in rats. Scientific Reports (2020).
4. Physiologic Measures of Animal Stress during Transitional States of Consciousness. Animals (2015).
5. Combining Nitrous Oxide with Carbon Dioxide Decreases the Time to Loss of Consciousness during Euthanasia in Mice — Refinement of Animal Welfare?. PLOS ONE (2012).
6. Attitudes of laboratory animal professionals and researchers towards carbon dioxide euthanasia for rodents and perceived barriers to change. Laboratory Animals (2021).
7. Intraperitoneal injection of sodium pentobarbital has the potential to elicit pain in adult rats (Rattus norvegicus). PLOS ONE (2020).