Animal research is rife with both human and non-human animal welfare concerns. In our recent Faunalytics Fundamental on Research Animals, we covered a variety of the welfare implications of keeping animals in laboratories (labs) and also looked at how findings from animal research may not translate to human medicine as well as we think. One reason for this is because animals like mice and rats that are bred in labs for many generations and housed in non-natural environments do not exhibit behavior that suggests they ever adapt to these conditions. This inability to adapt can negatively impact research results.

On the other hand, rats bred for years in captivity will still build nests when provided with nesting materials and dig burrows when given the chance. What’s more, when laboratory rats are housed in a semi-wild setting, they will “revert to a predominantly nocturnal activity pattern.” This last part is especially important, because even though rats and mice are “inherently nocturnal,” it iscommon to house and experiment on mice under bright, artificial lighting and during the hours of a human working day.

This opinion paper was written by researchers especially concerned with the effect of animal research on the circadian rhythm—or 24-hour physiological process—of rats and mice. They consider the potential negative impacts of human laboratory routines and lighting conditions on scientific validity and reproducibility. They note that rats and mice are most active during the “dark period” and exhibit a rise in activity just before the onset of darkness. Rats and mice will sleep in many short bouts throughout a 24-hour day, but there are “significantly more sleep bouts during the light period.” In contrast, lab animals are kept under artificial light for 12 hours during the day followed by a 12-hour dark period at night.

The researchers note that this artificial cycle in the lab has scientific implications: cognitive tests frequently differ between rats and mice tested during their subjective day times or night times, with cognitive performance improving when rats and mice are typically awake and active. Physiological performance also differs for rats taken out of their typical circadian phase. Finally, the authors note that there are animal welfare and ethical implications associated with “testing animals during their resting period.” Rats and mice seem to be more prone to stressors and anxiety when they occur during their resting period and may even exhibit more depression-like symptoms.

For animal advocates, the study shows that there may be even more animal welfare implications for keeping animals in labs than previously thought. Though it may be intuitive that inducing sleep deprivation in animals can negatively impact their welfare, just like with people, it is rarely discussed in scientific literature or anti-vivisection advocacy. Overall, this paper provides another example of how unethical and unreliable animal research can be.