A meta-analysis recently published in the journal BMC Biology (Cait et al., 2022) found that rats and mice housed in conventional laboratory cages have higher mortality rates and greater disease severity compared to rodents housed in “enriched” environments. This finding suggests that conventional laboratory housing causes chronic stress.
Previous research has already shown that conventional housing for rodents—which consists of barren or nearly barren shoebox-sized cages—restricts many natural behaviors and is associated with reduced welfare. Here, researchers tested whether conventional housing causes chronic psychological stress. To test their hypothesis, the team analyzed the results of numerous animal studies that compared mortality and disease outcomes in rodents housed in conventional versus “enriched” cages that better meet rodents’ behavioral needs. (From an initial 10,096 articles, 214 met the inclusion criteria, such as use of rats or mice and publication in English.)
The researchers focused on seven maladies that can affect both humans and rodents. In humans, it is known that these afflictions are exacerbated by chronic psychological stress. The researchers also looked at lifespan, which chronic stress is known to shorten in humans.
The results were clear: Conventionally housed rodents have a 50 percent higher probability of dying and a 9 percent lower median lifespan; they also have increased risk of developing cardiovascular disease, increased severity of cancer and stroke, and increased signs of anxiety and depression. (For two of the afflictions initially targeted—asthma and viral infections—the researchers did not find enough studies involving rodents to allow comparisons.)
The widespread and sanctioned use of laboratory housing that produces chronically stressed animals is alarming. Research industry assertions that they consider animal welfare a primary concern fall flat when the animals’ welfare is deliberately compromised at the outset. Moreover, the use of chronically stressed animals raises serious concerns about the generalizability and the validity of the data they generate.