Studies on happy mice produce results that are just as reproducible as those on stressed animals.© Alamy

Mice living in exciting environments still produce reliable and reproducible results when used in scientific experiments, according to a new study. The finding suggests that researchers could offer their lab animals more interesting surroundings.

Previous work has shown that mice living in standard, barren cages may suffer greater stress or exhibit abnormal repetitive behaviours¹. This uninspired housing has caused concerns over animal welfare, and the validity of experiments. Stress, for example, is known to interfere with learning and memory, as well as the immune system.

But regardless of this, scientists have hesitated to add exciting elements to mouse cages for fear that doing so would influence the precision and reproducibility of test results.

Although the reluctance is widespread, not everyone believes in this logic. “There have been no data substantiating these fears,” says Hanno Würbel, an ethologist at the University of Giessen in Germany. He and a team of researchers decided to investigate whether enriched cage environments compromised experimental outcomes.

Engaging ideas

To assess the influence of animal housing conditions, they ran behavioural tests on over 400 female mice. These experiments took place in three different labs and compared standard cages with more exiting ones.

Every few days the researchers introduced novelties such as tunnels, trapezes and tissues into the enriched cages, while the mice living in standard cages missed out.

As expected, Würbel and his colleagues found that the animals in enriched cages were more confident than those from the control group. One test, known as the O-maze, illustrated this fact clearly. An O-maze is a circular track elevated above the ground with protective areas on either side.

Generally, mice prefer to stay in the sheltered parts for fear of being exposed to the open, brightly lit parts of the track. The study demonstrated that mice who lived in stimulating environments spent about twice as much time in these exposed areas as compared with their control counterparts.

Enhanced view

But although researchers noticed a difference between mice from enriched and barren cages, crucially they found that results from the enriched group remained as stable across the three labs as those from the control group. In other words, increasing the animals’ quality of life did not make the results from different labs any more variable. The study is the first to assess such effects using simultaneous tests in multiple labs. The findings appear in this week’s Nature².

Exactly why are the mice housed in interesting cages less stressed? “No one knows the answer to this,” Würbel confesses. He speculates that animals feel more in control of their environment when they can respond to new threats. Mice living in enriched conditions, for example, have the option of hiding behind objects placed in their cages when scared by humans.

Enriched opinions

According to James Kirkwood, chief executive and scientific director of the Universities Federation for Animal Welfare, standardization of cages reduces the number of live mice needed for experiments. “For numbers to be kept to a minimum it is important that sources of variation are controlled,” he says. But he adds that “housing designed for the animals’ physical and behavioural requirements need not compromise this objective”.

Others believe that researchers miss the point altogether. “There is no avoiding that animals kept in laboratory conditions are significantly stressed, and no amount of enrichment studies will prevent this,” says Nicky Gordon, science officer at the British Union for the Abolition of Vivisection. “Rather than more studies involving the use of animals, what is needed is more research into non-animal alternatives.”

The new findings are unlikely to cause immediate changes in labs. “I think it will probably take some time until this is implemented on a broad scale,” Würbel says. Enriching lab-animal environments requires additional time and money. But he added that “from now on people can’t hide behind a scientific argument”. 

Ethologist at the University of Giessen in Germany

Science officer at the British Union for the Abolition of Vivisection

• References

  1. Chapillon, P. et al. Behav. Genet. 29, 41 - 46 (1999). | Article | PubMed | ChemPort |
  2. Wolfer, D. P. et al. Nature 432, 821 - 822 (2004). | Article | PubMed | ChemPort |