For animals in the wild, days and nights are not delineated via a flick of the switch on the wall. Rather, dawn brings on a gradual waxing of the light, and night falls in an extended, dusky fade to black. Conversely, in laboratory settings (unless the animals are housed in rooms exposed to natural light), day often begins with a jolt of intense light accompanied by the unannounced appearance of humans, and ends with abrupt darkness and sudden solitude.
Mindful of this contrast, OPR Coastal Primate Sanctuary founder and president, Polly Schultz (profiled in the Winter 2011 AWI Quarterly) was concerned that such stark day/night segmenting might boost stress levels for the monkeys in her care. She pondered what she could do to test this, and—if her hypothesis proved to be true—what she could do to alleviate the stress.
One measure of stress is the amount of cortisol produced by the body. Cortisol, in fact, is known as the “stress hormone” because—in addition to its other functions—it is secreted in higher levels during an animal’s “fight or flight” response, giving a quick burst of energy in times of acute need. Continuously elevated levels of stress—and cortisol—can have negative physiological and emotional effects, however. Though humans may not be conscious of our own cortisol levels, we are all too aware of how it feels to cross that emotional line and feel “stressed out” or unduly agitated with nowhere to run.
Schultz tested a total of eight monkeys at the sanctuary—six adult cynomolgus macaques (three males and three females) and two rhesus macaques (both male, a juvenile and an adult). Given that drawing blood to measure cortisol could itself be a stressor and skew the results, Schultz devised a plan to measure cortisol via saliva samples obtained surreptitiously, without restraining the animals. She then hooked up a gradual lighting system in her facility that simulates dawn and dusk phases, and proceeded to take numerous samples under standard on/off light switch conditions, during a transition phase, and during a period when the monkeys only experienced the gradual lighting system.
In reporting her results to research professionals on AWI’s online Laboratory Animal Refinement and Enrichment Forum, Schultz indicated that “the saliva cortisol concentrations were significantly lower during dawn and dusk phases compared to the same time where the lights were instantly switched on and off. With every monkey every time.” Cortisol levels were cut nearly in half, from an average 0.059 ug/dl under standard lighting conditions, down to 0.030 during the gradual lighting conditions. Informal staff observations supported the results: Under the gradual lighting system, Shultz says, the monkeys “…were significantly calmer and more relaxed. They all appeared in much better moods especially in the morning during feeding….”
The results obtained by Shultz provide further evidence that research facilities implementing simple yet innovative refinements—ones that strive to mimic natural conditions whenever possible—can improve the welfare of the animals in their charge.