UBC Theses and Dissertations

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UBC Theses and Dissertations

Current methods of mouse euthanasia : refinements and aversion Moody, Carly


Mice are routinely euthanized by gradual-fill carbon dioxide (CO₂) gas or with isoflurane; the aim of my thesis was to assess refinements to these procedures. The first study assessed the CO₂ method of euthanasia with the aim of minimizing the duration of dyspnea without exposing mice to painful concentrations (>40% CO₂). Various CO₂ flow rates (20, 30, 40, 50% cage vol/min) were used to examine the duration between the onset of dyspnea (identified by laboured breathing) and insensibility (identified by recumbency, loss of the righting reflex or loss of the pedal withdrawal reflex). The interval between the onset of dyspnea and loss of the righting reflex averaged 38.2 ± 2.4 s versus 59.2 ± 2.4 s, using 50% and 20% cage vol/min fill rates, respectively. Thus even at the highest flow rate tested mice experienced more than 30 s of dyspnea, suggesting other methods of euthanasia should be used when possible. The second study examined the same three measures of insensibility during the isoflurane method of euthanasia, with the aim of identifying when it is safe to switch to a high flow rate of CO₂, without subjecting conscious animals to painful concentrations. The results suggested that the onset of recumbency and loss of the righting reflex are not safe indicators of insensibility when using induction with isoflurane; continued induction with 5% isoflurane carried by 17% cage vol/min of oxygen for a minimum of 79 s after the appearance of recumbency is advised before switching to a high flow rate of CO₂. The final study in this thesis used a light-aversion test to examine mouse aversion to: 1) 20% gradual-fill CO₂, 2) 5% isoflurane administered using a vaporizer, and 3) 5% isoflurane administered using the drop-method. Mice chose to remain in the dark chamber longer when exposed to isoflurane administered using a vaporizer compared to both CO₂ and isoflurane drop. Mice were also more likely to become recumbent in the dark side when exposed to the isoflurane vaporizer versus other methods. These results indicate that isoflurane delivered by a vaporizer is a humane refinement for the euthanasia of laboratory mice.

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