Tiny cages make for sluggish lab rats

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Tiny cages make for sluggish lab rats

Everyone needs a stretch every now and then, but most lab rats don’t get the chance. According to new research, they are simply too confined in standard-sized cages to move naturally, potentially affecting their health and the outcomes of some experiments. Knowing that lab rat cages are a far cry from the rodents’ natural habitats, a team of scientists set out to observe the movements of some slightly more free-range rats. Most lab rats in the United States, Canada, and the European Union are housed in cages at least 18–20 centimeters tall, by regulation. But mature rats can reach almost twice that height when standing—between 26 and 30 centimeters. In the new experiment, scientists observed rats in much larger, multilevel habitats with a height of 125 centimeters. Compared with their tightly caged counterparts, who were unable to stand upright, 3-month-old rats stood an average of 178 times per day and 13-month-old rats stood an average of 73 times per day. They were also much more active: Three-month-old rats were seen climbing 76 times per day on average, whereas rats of all ages burrowed for about 20–30 minutes per day. The tightly caged rats, who don't have the space for these behaviors, seemed to stretch to make up for it, extending their bodies lengthwise nine times more often than rats housed in the larger cages, the scientists report today in Royal Society Open Science. The scientists say their findings are just the beginning of research into how standard laboratory cages may interfere with rats' normal movements. To find out how this may affect experimental results in fields like medicine and psychology, they say many more studies need to be done.