Like a person who stubs her toe, gets stuck with a needle or is otherwise put into an unpleasant position, animals express pain in their faces. We humans just don’t always recognize it. Now, researchers hope a new scale defining and measuring rabbit discomfort will help probing scientists recognize and avoid putting their bunny subjects through too much pain.
As Nature’s news team reports, scientists traditionally measured animals pain after the fact, looking at weight loss or conspicuous movements. So-called “grimace scales” hope to ward off excessive pain while it’s happening, though. In 2010, researchers announced a mouse and rat grimace scale, which the authors of this new PLoS One study used to develop the rabbit scale.
The researchers sorted pain responses into five “action units” such as narrowing of the eyes, abnormal ear movements, bulging of the cheeks and twitching of the whiskers. They then broke those action units down into a ranking scale of 0 (not present) to 2 (really present). The combined score quantifies the bunny’s total pain, as judged by the pain-inflicting humans.
The Swedish government encouraged the study in the hopes of assessing how painful ear tattooing—a common practice used to identify animals by numbers—is for rabbits. The researchers used their new scale to measure pain in rabbits tattooed without anesthetic, rabbits given a control treatment and rabbits given an anesthetic during the tattoo procedure. Since the rabbits’ ears couldn’t twitch properly while being tattooed, the highest possible pain score totalled 8 points rather than the usual 10. Rabbits tattooed with no pain killers scored 4 on the pain scale, while rabbits given the anesthetic scored less than 2 on the same scale.
Now that the scientists have confirmed that rabbits do indeed dislike being tattooed, they can incorporate pain killers into their tattooing routine. The team is also working on new pain scales for rhesus macaques, lambs, horses and pigs.
More from Smithsonian.com: