There’s a Major Issue With How We Treat Lab Mice, And It Could Affect Study Results

More than 120 million laboratory rats and mice are used worldwide every year. Many are accustomed to studying harrowing conditions such as cancer, arthritis and chronic pain, and nearly all spend their lives in small, empty box-like cages: a sort of permanent closure.

Our new analysis shows that this restrictive artificial housing causes rats and mice to become chronically stressed, altering their biology. This raises troubling questions about their well-being — and how well they represent typical human patients.

We identified this impact of housing by extracting data from more than 200 studies examining the effects of cage design on health outcomes known to be stress-sensitive in humans, such as death rates and disease severity such as cardiovascular disease, cancer and stroke. have been researched.

The importance of housing

The studies we all synthesized compared conventional “shoe boxes” — the small, bare-bones cages typical of labs — with better-equipped enclosures with running wheels, nest boxes, extra space, or other items that allow natural behaviors like digging, climbing, exploring. and hide.

Across the board, the animals in conventional cages got sicker than those in better equipped housing. For example, if they got cancer, they developed bigger tumors.

Conventionally housed animals were also at greater risk of death, with their average lifespan being shortened by about 9 percent. Scientists have known for decades that rats and mice want more comfort, movement and stimulation than is normally provided, and that is why conventional cages cause abnormal behavior and anxiety.

But this is the first evidence that they also cause chronic stress severe enough to endanger animal health.

When mice are kept in stimulating environments, they are healthier. (Aileen MacLellan/author provided)

Stressed Out Findings

Our study – like many others before us – also found evidence of methodological problems and poor reporting of experimental details. For example, the rodents used were biased by males, with few studies involving females.

Moreover, despite the housing effects research, two-thirds of the studies in our analysis did not fully describe animal living conditions. Our findings support many previous suggestions that rats and mice living in bare cages that lack stimulation may not be suitable models for several reasons. Laboratory animals are usually male, but also often overweight, sometimes chronically cold and cognitively handicapped.

We suspect that the reliance on “SMALL” animals – cold, round, abnormal, male-biased, enclosed and upset – could help explain the current low success rates of biomedical research. There are already examples of research studies yielding very different conclusions depending on how their animals are kept, and we now want to assess to what extent this is happening.

That housing is critical to rodent biology, but often poorly described in papers, could also help explain the “replicability crisis”: that at least 50 percent of preclinical research results cannot be replicated when other scientists rerun a study.

Racks with housed miceHousing is critical to the well-being of laboratory mice. (Understanding Animal Research/Wikimedia Commons)

Canadian policies

Only 1 to 2 percent of the world’s research animals live in Canada, so why should Canadians care? First, because this still means 1.5 million to two million animals are unintentionally stressed: something that anyone who cares about animals will find.

But if housing does indeed change the research conclusions, this also has financial implications. Canada spends approximately CA$4 billion a year on health research.

According to US estimates, if half of that is animal-based, of which only 50 percent are reproducible, Canada could spend about CA$1 billion a year on non-replicable animal studies.

And even if studies are replicable, well over 5 percent of them provide useful medical benefits for humans. This is in stark contrast to the Canadian public’s expectation that about 60 percent of animal work leads to new medicines for humans.

Canadian standards require mice to be provided with nesting material that can keep them warm, but is it time to improve them further?

The ‘shoeboxes’ in which rats and mice currently live should no longer be ignored as a neutral background, but should be seen as a determinant of health: one that we can adapt, improve and study. This would allow us to better model the diverse social determinants of human health while improving animal welfare. The conversation

Georgia Mason, professor, integrative biology, University of Guelph and Jessica Cait, graduate student, integrative biology, University of Guelph.

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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