'Sacrifice' for science, lab rats are under heavy stress

Currently, more than 120 million lab rats are used worldwide each year. Many of them are used to studying conditions like cancer, arthritis, and chronic pain. Nearly all of them spend most of their lives in small, empty cages and are permanently locked in that environment.

New analyzes from scientists show that these restrictive artificial housing environments expose lab rats to chronic stress, altering their natural biomechanics. This in turn raises disturbing questions about the well-being and underrepresentation of the typical patient.

The researchers determined the effects of housing by extracting data from more than 200 studies that investigated the impact of cage design on health. This is known to be very sensitive to stress in humans, such as mortality and the severity of diseases such as cardiovascular disease, cancer and stroke.

In general, caged animals often become sicker.

The studies that were aggregated all compared the most typical conventional, barren, and rudimentary rat cages in the laboratory, with better-conditioned "houses" such as wheeled cages, boxes nesting, additional spaces, or other items that enable natural behaviors such as digging, climbing, exploring, and hiding in rats. In general, caged animals often become sicker than those in better conditions. For example, if they have cancer, they have developed larger tumors.

Animals that are kept indoors for too long are also at a higher risk of death, with their average lifespan dropping to about 9%. For decades, scientists have also known that rats and mice want more comfort, exercise, and stimulation than is normally provided. Therefore, when kept in experimental cages, they show signs of anxiety, stress and cause abnormal behaviors.

But this is the first evidence that austerity in captivity causes chronic pain, severe enough to affect an animal's health.

When rats were housed in a stimulating environment, they were healthier

The scientists' new research and previous studies have also found a lot of evidence, around methodological issues and detailed experimental reports. For example, the rodents used are predominantly male, with very few studies using female animals.

Furthermore, despite investigating the effects of housing, two-thirds of the studies included in the analysis did not adequately describe the living conditions of the animals. These new findings support the hypothesis that mice living in barren cages lacking stimulation may not be the right model. Study animals are usually male, overweight, and many have chronic cold and cognitive impairment.

The researchers suspect that reliance on so-called "CRAMPED" animals — cold, overweight, abnormal, male-biased, withdrawn, and miserable — could explain the low success rates. current biomedical research. There have been many examples of studies that have come to quite different conclusions depending on how the animals were kept. The new study aims to assess the extent to which this occurs.

Housing plays a very important role in rodent biology, but is often poorly described in the papers, which itself may help explain the "renewability crisis": less At least 50% of preclinical results cannot be reused or reproduced when other scientists do a similar study.

Housing is very important for the health of lab rats.

Canada currently has only about 2% of all laboratory animals worldwide. Canada spends about $4 billion a year on health research. It is estimated that if half of those are animals, of which only 50% are fertile, then Canada could end up spending about $1 billion a year on non-reproducible animal studies.

Canadian standards require rats to be provided with nesting material that can keep them warm, but is it time to improve them further? The type of cage in which the mouse is currently living is considered a determinant of health. And doing so will allow researchers to better model the diverse social determinants of human health, while also improving the health of animals.