Researchers at Newcastle University in the United Kingdom and the University of Guelph in Canada this week released the Rabbit Grimace Scale—an attempt to quantify the pain felt by laboratory rabbits during routine ear tattooing used to mark individuals. A previously released grimace scale study on mice has been shown to be an effective way of measuring the animals' pain and discomfort, and has been quickly adopted by researchers to access post-operative pain in laboratory rodents.

Before and after both sham and real ear tattooing, the researchers measured behavioral changes—including whisker movement, narrowed eyes, and cheek and nose bulging—on a scale of 0 to 2, with 0 being no discernible change and 2 being obvious discomfort. A combined score out of 8 indicates total pain. When a rabbit was tattooed without anaesthetic, the Rabbit Grimace Scale averaged 4, but with the addition of a local anaesthetic, the rabbits averaged a...

"The only way you can alleviate pain is to be able to identify it, and to understand how much pain an animal is in,” Matthew Leach of Newcastle University in the U.K., who helped develop this scale, told Nature. "There is a broad interest in grimace scales” for all sorts of lab animals, he added, noting that his team is currently developing a grimace scale for rhesus macaque monkeys.

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