Aversion to carbon dioxide

conducted at the University of British Colombia. These studies have used the gradual fill methods proposed by the American Veterinary Medical Association (AVMA) in an attempt to further clarify aversion associated with carbon dioxide. We have contacted the authors of this work and understand that they will also be responding to Dr Wood’s letter. Therefore, we will leave the discussion of these proposed methods and their findings to them. Finally, in the absence of conclusive evidence in Dr Wood’s letter, we are not convinced that he is correct in concluding (stated as his belief) that euthanasia of laboratory rodents with carbon dioxide is humane. We feel that this conclusion fails to take into account the wealth of literature supporting the aversiveness of carbon dioxide. We refer to the use of carbon dioxide as an ‘accepted’ pain stimulus in pain studies involving humans and other species (Thürauf et al. 1991, Komai & Bryant 1993, Peppel & Anton 1993, Danneman et al. 1997). Therefore, when all of this information is taken into account, the balance of evidence does seem to indicate that carbon dioxide is not a humane method of euthanasia. We also feel that until conclusive experimental evidence can be provided that carbon dioxide can be used humanely, the only humane action is to stop using carbon dioxide to induce unconsciousness and death in animals in the currently accepted protocols.