Voluntary Oral Ingestion of a Sedative Prior to Euthanasia with CO2: Behavioural Responses of Mice

Abstract

Laboratory mice are commonly euthanised with carbon dioxide (CO2); however, there is ample evidence that this gas is aversive. Previous work suggests that sedation achieved via injection with benzodiazepines prior to CO2 administration could reduce aversive behaviours during euthanasia. We explored the potential of using a voluntarily ingested sedative (tiletamine-zolazepam, Zoletil®) prior to euthanasia. Male and female C57BL/6 mice were allocated into one of the five experimental groups, which differed in the dose of Zoletil: 0, 10, 20, 40, 80 or 100 mg/kg. A dose of 20 mg/kg was found to achieve mild sedation prior to euthanasia; mice which received this dose numerically reared and walked on the cage lid less, and showed ataxia, immobility and recumbency for longer than mice that received a lower dose. During euthanasia, mice that received 20 mg/kg showed fewer aversive responses to CO2. Doses of 40 to 100 mg/kg were associated with signs of moderate to severe sedation, but resulted in an incomplete intake of the sedative, which made the interpretation of the aversiveness to CO2 difficult. Voluntary oral administration of a sedative is an effective, affordable, and easy way to minimize the stress of mice to euthanasia with CO2.

Evaluation of New Approaches to Depression Treatment Using an Animal Model of Pharmacoresistant Depression

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Rat Grimace Scale as a Method to Evaluate Animal Welfare, Nociception, and Quality of the Euthanasia Method of Wistar Rats

“…Some authors have proposed oral administration for premedication before the actual euthanasia method to refine euthanasia. For example, Rodríguez-Sánchez et al [84] recommended the use of oral tiletamine + zolazepam before euthanasia to induce sedation and decrease aversion. Nonetheless, Dudley and Boivin [85] found in mice that orally ingested pentobarbital solution in cookie dough did not induce LORR, unconsciousness, or death.…”

Striving for humane deaths for laboratory mice: hypobaric hypoxia provides a potential alternative to carbon dioxide exposure

“…A pharmacological approach was adopted to further elucidate the animals’ likely experience during the conscious phase and facilitate interpretation of the likely causation of spontaneous behaviour. Despite the evidence that animals exposed to CO 2 experience pain and distress, to our knowledge, few studies have used the application of pharmacological compounds such as analgesic and anxiolytic intervention in a welfare context for rodents [ 20 , 25 – 27 ]. By comparing hypobaric hypoxia with industry standard application of CO 2 , in addition to exploring the potential of hypobaric hypoxia, we also provide novel insights as to the likely experiences of mice exposed to CO 2 killing.…”