Evaluating methods of gas euthanasia for laboratory mice

The effect of carbon dioxide flow rate on the euthanasia of laboratory mice

“…In addition, a series of studies have now shown that rodents do not willingly tolerate exposure to similar CO 2 concentrations. [15][16][17][18][19][20][21] Therefore, if CO 2 is used to kill rodents, refinements to minimize distress during this procedure are important.…”

“…13,14 In the veterinary literature, dyspnea typically refers to labored breathing in animals, as currently labored breathing is associated with a negative affective experience in mice or rats. However, previous studies in mice and rats have shown that CO 2 concentrations ranging from 3-20% are aversive, [15][16][17][18][19][20][21] concentrations between 10 and 35% have been shown to cause fear responses, [22][23][24] and 10% CO 2 may be used as an 24 In the current study, labored breathing was directly assessed but we cannot be certain that this behavior was associated with a negative affect. However, on the basis of human evidence and the rodent research on aversion and fear responses, we posit that this autonomic response is accompanied by a negative affective experience.…”

Preanesthesia, Anesthesia, Analgesia, and Euthanasia

“…Additionally, altricial neonates require an extended period of CO 2 exposure, which may need to be followed by a physical adjunctive method of euthanasia (Klaunberg et al, 2004;Pritchett-Corning, 2009). There remains controversy regarding the recommended administration rate of CO 2 and the potential benefit for administration of isoflurane anesthesia or other gases or even injectable tranquilizers, sedatives, or anesthetics prior to, or in combination with, CO 2 (Hackbarth et al, 2000;Weary, 2006, 2007;Makowska et al, 2008Makowska et al, , 2009Chisholm et al, 2013;Wong et al, 2013;Leach et al, 2002aLeach et al, ,b, 2009Valentine et al, 2012;Makowska and Weary, 2009a,b;Makowska et al, 2012;Niel et al, 2008a,b;Thomas et al, 2012a). There remains controversy regarding the recommended administration rate of CO 2 and the potential benefit for administration of isoflurane anesthesia or other gases or even injectable tranquilizers, sedatives, or anesthetics prior to, or in combination with, CO 2 (Hackbarth et al, 2000;Weary, 2006, 2007;Makowska et al, 2008Makowska et al, , 2009Chisholm et al, 2013;Wong et al, 2013;Leach et al, 2002aLeach et al, ,b, 2009Valentine et al, 2012;Makowska and Weary, 2009a,b;Makowska et al, 2012;Niel et al, 2008a,b;Thomas et al, 2012a).…”

Response to Roustan et al. ‘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

“…Nonetheless, it has been demonstrated that isoflurane is less aversive than other gaseous or volatile euthanasia agents including carbon dioxide, 2 the most commonly used agent, and for this reason its use has been suggested as a more humane inhalation technique. 2,5 Isoflurane may be the 'least worst' option when an inhalation method of euthanasia must be used, but the presumption of Roustan and colleagues that euthanasia with isoflurane is more humane than a physical method such as cervical dislocation is questionable. To the best of my knowledge it has not been shown that euthanasia with isoflurane is more humane than physical methods.…”

“…Mice as well as rats will generally forego a highly desired food reward to avoid isoflurane exposure. 2,3 When an aversive stimulus is inescapable and an animal cannot adapt to the stressor (as is the case during induction of isoflurane anaesthesia) it is likely that some degree of distress will result. 4 An ideal euthanasia agent would be one which would cause death without pain or distress; 5 -7 therefore, isoflurane does not appear to fulfil the criteria for such an ideal agent.…”