Effective alleviation of pain in laboratory animals depends on the ability to recognise pain and assess its severity. Traditional methods of pain assessment based on monitoring of behaviour and clinical signs, such as weight loss, are time consuming and can have other limitations - for example, the signs observed may not be specific to pain.
Facial expressions are considered the gold standard for pain assessment in non-verbal humans, such as infants, and are beginning to be used to assess pain in laboratory rodents. This follows the work of Dr Jeffrey Mogil at McGill University who developed 'grimace scales' for measuring pain intensity in the mouse and the rat. Each scale is based on changes in a number of facial 'action units', such as narrowing of the eyes (orbital tightening), and bulging or flattening of the cheeks and nose.
For the first time, and with NC3Rs funding, researchers at Newcastle University have established a Rabbit Grimace Scale, to enable more effective and faster pain assessment in these animals. The scale was developed by Dr Matt Leach and colleagues using data from a study commissioned by the Swedish Board of Agriculture on clamp tattooing of the ear - a procedure commonly used to identify farmed rabbits. Published in PLoS ONE, the work demonstrates that signs such as orbital tightening and changes in the position and shape of the whiskers reliably indicate acute pain and correlate with physiological signs of stress, such as increased heart rate.
Dr Leach's team is now collaborating to develop grimace scales for other species, such as rhesus macaques, sheep, pigs and horses.
Posters of the Rabbit Grimace Scale are coming soon, and will be provided by NC3Rs to research establishments using and breeding rabbits. Other posters, such as Rat and Mouse are available now at our Grimace Scale hub.
Keating SCJ, Thomas AA, Flecknell PA, Leach MC (2012) Evaluation of EMLA cream for preventing pain during tattooing of rabbits: Changes in physiological, behavioural and facial expression responses. PLoS ONE 7(9): e44437.
Left to right, as pain increases, the orbits of rabbit's eyes narrow. This is one of five facial action units in the Rabbit Grimace Scale. Reproduced with permission.