Jasmine Clarkson*, Jessica Martin, Julian Sparrey, Francesco Marchesi, Matthew Leach, Dorothy McKeegan

*Corresponding author for this work

Research output: Contribution to conferenceAbstractpeer-review


Mice are the most widely used laboratory species, with millions used annually worldwide. The vast majority of
these are killed either during or after the scientific work and, according to current legislation, must be killed
humanely. Exposure to a rising concentration of carbon dioxide (CO ) remains the most common method of killing
laboratory rodents, despite significant welfare concerns surrounding its use, including its ability to induce anxiety,
dyspnoea, and pain at high concentrations. Therefore, there is an urgent need to find a humane, practical, and
high-throughput alternative.
We are systematically investigating whether hypobaric hypoxia (via gradual decompression, a process equivalent
to ascending to high altitude) could be a novel and humane approach to the killing of laboratory mice due to its
insidious onset in humans. Hypobaric hypoxia occurs at low atmospheric pressures due to a proportional
decrease in the partial pressure of oxygen, and exposure to these environments leads to progressive loss of motor
and cognitive function and ultimately unconsciousness and death.
The goal of this trial was to determine the behavioural consequences of hypobaric hypoxia in conscious mice using a decompression profile designed to avoid the risk of barotrauma based on previous work. We investigated the effects of a terminal treatment: gradual decompression, CO and a SHAM treatment (no killing method applied) and employed the use of pharmacological interventions to infer the likely welfare consequences in a 3x3 factorial design. Within each treatment, mice were administered analgesia (Buprenorphine, 0.05mg/kg), anxiolytic
(Diazepam; 2.5mg/kg) or saline at equivalent volumes.
We found significantly elongated latencies to hypoxia and death in mice undergoing decompression compared to CO , however mice exposed to decompression exhibited a more ‘normal’ behavioural repertoire in line with SHAM mice. Decompression was associated with greater levels of ear scratching compared to SHAM and CO mice, although only 33% of mice performed this behaviour. Ear scratching was unaffected by analgesia and anxiolytic intervention and therefore unlikely to reflect anxiety and/or pain. Exposure to CO was associated with significantly more gasping which was mediated by analgesia and anxiolytic treatments and therefore likely to be associated with dyspnoea and air hunger. We also found more active escape attempts in mice undergoing CO (n=3; all saline treated mice), compared to decompression (n=1).
We discuss our findings in relation to the likely welfare impacts of gradual decompression and conclude that it may have potential to provide a high welfare method of killing laboratory mice.
Original languageEnglish
Publication statusPublished - 28 Jun 2022
EventUFAW Advancing Animal Welfare Science 2022 - Edinburgh
Duration: 28 Jun 202229 Jun 2022


ConferenceUFAW Advancing Animal Welfare Science 2022
Internet address


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