Responses of Male C57BL/6N Mice to Observing the Euthanasia of Other Mice.

The AVMA Panel on Euthanasia recommends that sensitive animals should not be present during the euthanasia of others, especially of their own species, but does not provide guidelines on how to identify a sensitive species. To determine if mice are a sensitive species we reviewed literature on empathy in mice, and measured the cardiovascular and activity response of mice observing euthanasia of conspecifics. We studied male 16-wk-old C57BL/6N mice and found no increase in cardiovascular parameters or activity in the response of the mice to observing CO2 euthanasia. Mice observing decapitation had an increase in all values, but this was paralleled by a similar increase during mock decapitations in which no animals were handled or euthanized. We conclude that CO2 euthanasia of mice does not have an impact on other mice in the room, and that euthanasia by decapitation likely only has an effect due to the noise of the guillotine. We support the conceptual idea that mice are both a sensitive species and display empathy, but under the controlled circumstances of the euthanasia procedures used in this study there was no signaling of stress to witnessing inhabitants in the room.