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Strategic grant

Assessing the humaneness of gas euthanasia techniques for laboratory rodents

An orange Eppendorf rack partly full of PCR tubes.

At a glance

Award date
July 2010 - December 2013
Grant amount
Principal investigator
Dr Huw Golledge


Newcastle University


  • Refinement

Application abstract

Most laboratory rodents are killed with carbon dioxide (CO2). There is general consensus that CO2 causes aversion - but disagreement as to how significant this is, nonetheless it has been suggested that CO2 should be replaced by volatile anaesthetics, e.g. Isoflurane. If CO2 is to be replaced, it is essential that the replacement is demonstrably more humane. If CO2 use is to continue, it is imperative that we understand which method of delivery represents best practice. We will answer two key questions: 1) How aversive is CO2 compared to other methods? We will use a conditioned place avoidance paradigm to compare the relative aversiveness of CO2 and Isoflurane against known unpleasant stimuli (predator odour, cold etc). 2) Could CO2 or Isoflurane be applied in a less stressful way? Stress associated with euthanasia may be enhanced by moving animals to a euthanasia chamber. We will examine whether mice could be exposed to COin a less stressful way by carrying out the process in their home cages whilst relaxed (or sleeping). At the end of the study we will organise a consensus meeting to disseminate results to stakeholders to ensure that any findings contribute as rapidly as possible to improvements in practice.



  1. Hawkins P et al. (2016). A Good Death? Report of the Second Newcastle Meeting on Laboratory Animal Euthanasia. Animals 6(9):50. doi: 10.3390/ani6090050
  2. Thomas AA et al. (2012). Combining nitrous oxide with carbon dioxide decreases the time to loss of consciousness during euthanasia in mice – refinement of animal welfare? PLOS ONE 7(3):e32290. doi: 10.1371/journal.pone.0032290 
  3. Makowska J et al. (2012). Comment on ‘Sedation or inhalant anesthesia before euthanasia with CO2 does not reduce behavioral or physiologic signs of pain and stress in mice’. Journal of the American Association for Laboratory Animal Science 51(4):396–397. PMC3400683
  4. Golledge HDR (2012). Comment on Roustan et al. (2012) ‘Evaluating methods of mouse euthanasia on the oocyte quality: cervical dislocation versus isoflurane inhalation’: Animal welfare concerns regarding the aversiveness of isoflurane and its inability to cause rapid death. Laboratory Animals 46(4):358–359. doi: 10.1258/la.2012.012101