Nitrogen gas less aversive during euthanasia compared with carbon dioxide, study shows

Researchers at the University of Zurich, ETH Zurich and Animal Park Goldau showed that nitrogen gas produced lower behavioural activity and electrophysiological reactions during euthanasia compared to carbon dioxide. Nitrogen may be less aversive than carbon dioxide, although it may still cause some degree of fear response, they found. The study also demonstrated that rapid-fill carbon dioxide causes less aversive behavior than slow fill. Researchers are trying to find more suitable euthanasia agents than carbon dioxide for mice. Carbon dioxide, the most widely used euthanasia agent, is fast-acting, cheap and easily available, but it may cause distress and anxiety.
More info: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0210818