Almost all people live in cramped boxes as part of a temporary shutdown in the laboratory rats and mice worldwide. Many are used to investigate distressing conditions such as cancer, arthritis, and chronic pain.
This new study shows that this restrictive, artificial housing causes rats and mice to become chronically stressed, modifying their biology. This raises worrying questions about their welfare and the way they represent typical human patients.
Results from over 200 studies that examined the effects of cage design on health outcomes that are stress-sensitive for humans, such as mortality rates and the severity of cardiovascular disease, cancer, and stroke, have revealed this effect of housing.
The importance of housing
All of the experiments we analyzed used "shoeboxes," primarily small, barren cages used in labs with better-resourced housing containing running wheels, nest boxes, additional space, or other items that enable natural activities like digging, climbing, exploring, and hiding.
Animals living in traditional cages became sicker than ones living in better-resourced homes. For example, if given cancer, they developed larger tumors.
Animals living on conventions were at an all-time high, with their average lifespans reduced by about 9 percent. Scientists have discovered that rats and mice desire more comfort, exercise, and stimulation than they are normal, and that conventional cages therefore stimulate abnormal behavior and anxieties.
The first evidence that they may also cause chronic distress, especially if they do not affect animals'' health.
When mice are contained in stimulating environments, they are healthier. (Aileen MacLellan/Author provided)
Similar to many others previously, our research also found evidence of methodological problems and poor reporting of experimental findings. For example, the rodents used were male-biased, with only studies employing female animals.
Despite examining housing implications, two-thirds of the findings were incomplete in terms of animal living conditions. Many previously suggested that rats and mice living in barren cages without stimulation may not be suitable models, for several reasons. Typically male, as well as often chronically cold, and cognitively impaired.
The growing use of "CRAMPED" animals in biomedical research may help explain the current low success rates, including evidence of research studies making quite different conclusions depending on how their animals are held, and we now aim to investigate the extent to which this occurs.
As other researchers re-run a research, housing is vital for rodent biology, although often poorly described in papers. Moreover, the "replicability crisis" might be explained, since at least 50 percent of preclinical research findings cannot be replicated.
Housing is crucial for the well-being of laboratory mice. (Understanding Animal Research/Wikimedia Commons)
Only 1 to 2 percent of the world''s research animals live in Canada, so why should Canadians pay attention? One thing, because 1.5 million to two million animals are being unintentionally stressed, which is something that anyone who cares about animals will find.
If animal housing does indeed alter research conclusions, then that may have financial implications. Canada invests roughly CA$4 billion in health research every year.
According to US estimates, if half of that is animal-based, of which only 50 percent is reproducible, then Canada might spend around CA$1 billion per year on non-replicable animal research.
Even if studies are replicateable, well below 5 percent of them provide useful medical benefits for humans. This is a significant contrast to the Canadian public''s expectation that approximately 60 percent of animal work would result in new human medicines.
Can mice be provided with nesting materials that can keep them warm, but is it time to improve them even further?
The "shoeboxes" that rats and mice currently inhabit should be avoided as if it were a neutral backdrop, and instead of being seen as a determinant of health. Doing so would enable us to better model human health and improve animal well-being at the same time.
Georgia Mason, a doctoral student in Integrative Biology at the University of Guelph, is a graduate student in Integrative Biology at the University of Guelph.
This article is republished from The Conversation under a Creative Commons license.