'Happy' mice skew results

Mice are used to develop medical treatments

By BBC News Online's Ania Lichtarowicz

Improvements in animal welfare in scientific laboratories are having an unexpected effect on test results.

Even just adding a tube to let mice run through delayed the visible onset of the disease

Dr Emma Hockly

Researchers believe that because rats and mice are so well treated these days, the animals now respond slightly differently to the tests carried out on them.

This could make it more difficult to compare the results of modern experiments with those conducted many years ago.

It could also mean more animals have to be used in procedures to get statistically significant results - at least in the short term.

New guidelines

Animal welfare conditions have improved substantially in recent years and the European Commission is planning new guidelines for further changes.

Different animals will need different improvements - for instance, mice will need nesting places, while guinea pigs will require hiding boxes like tubes or pipes.

But by improving living conditions, scientists are inducing changes in animals' behaviour. Dr Emma Hockly, from King's College, London, UK, has been studying how an improved environment affects behaviour in mice that carry a gene for Huntington's disease.

"A very low level of enrichment - for instance, even just adding a tube to let mice run through - delayed the visible onset of the disease," she told BBC News Online.

This, reports New Scientist magazine, presents a problem for scientists who might take 15 years to develop a drug. The animals used in their latest research work are behaving differently to those used in the initial experiments.

Genome project

This could skew the final outcome of the research.

Dr Hockly said that better animal welfare was obviously desirable but added that more experiments might need to be carried out in the short term to compare old and new living conditions to factor into the end research.

However, once this was done, Dr Hockly said, the tests would be better as the animals would be living more like humans, and the animal "models" would be more realistic.

Investigations following on from results of the project to decode the human genome are expected to greatly increase the numbers of mice and rats used in laboratory experiments.

In the year 2000, about 2.7 million procedures were carried out on animals, compared with more than five million in 1976.

More than 80% of these experiments involved the use of rodents.