While politicians fret about euthanasing humans, bench scientists in the US and UK are having bunfights over euthanasing mice. According to Nature, tens, perhaps hundreds, of millions of mice are killed every year in labs around the world. The number is on the rise, too, because of the need for specially bred transgenic mice for medical research. The most common method of execution is gassing the rodents with CO2, followed by a procedure which breaks the animal’s neck. However, some researchers regard this as cruel because it appears to cause the animal some distress and it could be painful. A conference at the University of Newcastle upon Tyne, in the UK, was convoked in February to discuss the most humane method of euthanasing rodents.

The European Commission is also revising a directive on lab-animal welfare at the moment. It may instruct researchers to use anaesthesia before killing with CO2 and advise that killing with CO2 alone should be phased out as soon as possible. However, change will not be easy, as the present method is clean, well established and cheap. Alternatives include anaesthetic gases, guillotining, and argon gas — but no one is suggesting the household mouse trap.