Let Them Play: How Richer Home Environments Make Mice More Social

A C57Bl/6 mouse, one of the most commonly used mouse strains in biomedical research.

If they could talk, the animals in our farms, laboratories, zoos, and homes might have a word to say about their living conditions.

Raising mice in conventionally barren cages leads to more aggressive and less sociable animals, according to a recent study by PhD student Lindsey Kitchenham and Dr. Georgia Mason, a behavioural biologist in the Department of Integrative Biology. Not only that, but outside mice could distinguish mice from barren cages and, in one strain, would even respond with hostility.

Mason had witnessed this sort of behaviour before and wanted to know more.

“We wanted to know why barren-housed animals are less sociable by testing a few hypotheses: that it was related to being aggressive or aggressed, or that it was predicted by repetitive behaviours and inactive, depressive-like sitting,” says Mason.

The setup of the study allowed them to compare how lifelong housing conditions would affect behaviour both inside and outside the cages. Female mice—who, Mason explains, are generally more social than males—were raised in either conventional barren cages or well-resourced cages, where they could engage in natural exploratory behaviours like climbing, running, and nest-building.

According to Mason, the barren housing conditions experienced by the study animals are the norm, not the exception.

“Conventional mouse cages are typically called ‘shoeboxes’—they’re small and have woodchip-sawdust bedding on the floor, some nesting material, and transparent sides. It’s a bit like living your whole life in a transparent room with a carpet, a bed, and two other women.”

The well-resourced cages were markedly different. They were larger and included components like running wheels, plenty of nesting material, and ladders and pine cones to climb on. Mason describes these cages as complex, three-dimensional spaces where the mice simply have more things to do. And although the well-resourced cages ostensibly contained more unique and desirable items, the mice got along better.

“They’re less aggressive to each other, even though they have more to fight over,” says Mason. “The more you give them, the less they compete, and they were more social with strangers. It’s unambiguously good.”

In barren cages, on the other hand, the mice became increasingly antisocial.

“Conventionally housed mice were constantly sniping at each other, even though they had the exact same resources,” says Mason. “And aggression against their cage mates was one of the factors that predicted their low sociability to outsider mice.”

What’s more, outsider mice could tell which experimental mice had been raised in conventional cages, though exactly how they do so remains to be explored.

In addition to their social differences, the mice living in shoebox cages started to show signs of a depressive-like, inactive state and would even ‘barber’ each other—that is, pluck out each other’s whiskers and fur.

Mason notes that the phenomenon whereby poor housing conditions increase aggression and antisocial behaviour is not restricted to laboratory mice.

“In zoos, for example, animals are brought together at huge expense, but the breeding often fails,” she notes. “If we raise animals in suboptimal conditions, are we making them sexually and socially unattractive?”

Mason draws a further parallel between how captive animals are kept and our collective experience during the pandemic, where we saw firsthand that having only our most basic needs met severely impacted our quality of life.

“Look at how socially odd many of us were emerging from lockdown. It was clear that being protected from disease and having our homeostatic needs met was not enough,” Mason points out. “A lot of captive animals live in lifelong lockdown conditions.”

While Mason hopes that this study will help bring about changes in how animals are kept in captivity, she adds that improving living conditions for laboratory animals in particular might promote research efficiency.

“Current conventional housing conditions mean that studies extrapolate results from chronically stressed mice. But conclusions can actually flip according to housing type,” says Mason. “The inefficiency of the animal testing system means it takes longer to find genuine treatment, during which time patients are waiting—and dying.”

From increasing the efficacy of taxpayer-funded research to improving the success rate of conservation breeding programs, enriching the lives of captive animals means keeping them both healthy and happy. Simple changes that give animals the opportunity to interact and play is, as Mason puts it, unambiguously good. And from mice to humans, we all stand to gain from getting along a bit better.

This study was funded in part by the Natural Sciences and Engineering Research Council and the Ontario Graduate Scholarship program.

Read the full study in the journal Applied Animal Behaviour Science.

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