The aim of the present study was to define at what time point animal is dying and how quickly changes in the function of brain and heart can be observed. Four groups of sedated standard dark male mink (Mustela vison) were tested: euthanasia with filtered exhaust gases (CO concentration in the killing box 4%, 8 animals), carbon dioxide (CO2 from a cylinder, concentration in the killing box 80%, 8 animals), carbon monoxide (CO from a cylinder, concentration in the killing box 4%, 9 animals) and euthanasia with carbon monoxide (CO from a cylinder, concentration in the killing box 2%, 6 animals). Brainstem auditory evoked responses (BAER), electroencephalography (EEG), electrocardiography (ECG) and respiratory rate were measured before and during euthanasia. Mean time of decline/absent BAER was 112/176, 138/183, 235/390 and 528/833 seconds after gas application in groups, respectively. Mean time for first changes/absence of EEG was 42/86, 39/75, 55/190 and 176/426 seconds after gas application in groups, respectively. Mean time for first changes in respiration/absent breathing was 42/217, 28/227, 144/477 and 331/901 seconds after gas application in groups, respectively. Mean time for first changes/absence of ECG was 105/292, 117/220, 215/289 and 481/682 seconds after gas application in groups, respectively. Our results indicate that the studied gases first affect brain and brainstem which was seen as loss of EEG and BAER and just thereafter respiration and heart rate in turn. While sensitivity to pain is essentially related to consciousness and function of brain, gases can be considered to primarily and effectively lead to state of non-pain. Particularly the death with the filtered exhaust CO and the cylinder CO2 gases occurs quickly and in very comparable times. The euthanasia with the cylinder CO of 2% concentration seems to be too long and is most likely not suitable for the mink euthanasia in general. Observable signs of marked irritation or aversion were not found during exposure to studied CO and CO2 gases.
