'Mouse massacre' in labs

Up to 99% of mice bred for gene experiments can be killed

UK bioethicists are expressing concern over the large and rapidly rising number of laboratory mice being slaughtered as "waste" by genetic engineers.

Only between 1% and 10% of mice successfully incorporate the DNA which the experimenters inject into their embryos, says New Scientist magazine. Those that do not are killed.

One senior animal technician at a leading British university told New Scientist being asked to kill so many animals upset her. "I go away feeling physically and emotionally exhausted, and I think it's important for people to understand how we feel."

Laboratory animals have always had to be destroyed and the number of laboratory animals being used in scientific experiments overall is decreasing. But the numbers of transgenic mice is rising.

In 1990, fewer than 50,000 experimental procedures in the UK used genetically altered mice. In 1997, the figure was well over 300,000.

Scientists create transgenic mice to unlock the genetic secrets of development and so they can study human diseases in animal models. Many biologists believe this technology will bring major advances in medicine.

Missing mice

The Home Office controls animal experiments in Britain and says the "waste" animals should be included in the official statistics. But some observers believe many are being left out.

"It's very difficult to work out the exact number killed surplus to requirements," said David Morton, head of the centre for biomedical ethics at the University of Birmingham.

"I think a lot of people may cull them and not count them," he told New Scientist.

Trying to re-use the tissue of the unwanted mice in other experiments is unlikely to be practical. The laboratories involved are widely scattered and working to different timetables.

Until a more reliable way of inserting genes into mice is developed, the slaughter is likely to continue.

In the meantime, Dr Morton believes scientists must carefully consider the consequences of the culls on the technicians who have to perform them.