We all use facial movement to express pain and suffering and to recognise it in other humans. Scientific measurement of facial expression is in fact widely used to measure pain in infants which cannot express their feelings verbally (Schiavenato, 2008).
Research is now being conducted into the recognition and interpretation of facial expressions in a number of animal species. This will help researchers both to recognise pain and suffering, and also to assess the efficacy of pain treatment.
Grimace scales have been developed for 10 species: the mouse, rat, rabbit, cat, horse, cow, piglet, sheep/lamb, ferret and seal. See Mogil et al. (2020) for an overview. Researchers are working on similar scales for the rhesus monkey.
Similar research has been performed on cows to assess their degree of contentment using a range of welfare indicators, including the size of the white of the eye (Sandem et al., 2002) and the posture of the ears (Proctor & Carder, 2014). Studies have been performed on goats to detect signs of emotions in both positive and negative situations (Briefer et al., 2015).
More resources for planning animal research and testing are available in the PREPARE guidelines.
- Mota-Rojas D et al. (2020) The Utility of Grimace Scales for Practical Pain Assessment in Laboratory Animals. Animals, 10(10), 1838.
- Mogil J et al. (2020): The development and use of grimace scales for pain easurement in animals. Neur. Bio.Rev. 116, 480-493.
- McLennan et al., (2019): Conceptual and methodological issues relating to pain assessment in mammals: The development and utilisation of pain facial expression scales
- McLennan K & Mahmoud M (2019): Development of an Automated Pain Expression Detection System for Sheep (Oves Aries). Animals, 9, 196
- Merkies K, Ready C, Farkas L & Hodder A (2019): Eye Blink Rates and Eyelid Twitches as a Non-Invasive Measure of Stress in the Domestic Horse. Animals 9(8), 562.
- Zhang et al. (2019): Influence of Rater Training on Inter- and Intra-rater Reliability When Using the Rat Grimace Scale
- Häger C, Biernot S, Buettner M, Glage S, Kuebler LM, et al. (2017): The Sheep Grimace Scale as an indicator of post-operative distress and pain in laboratory sheep PLoS ONE doi: 10.1371/journal.pone.0175839
- Lu Y, Mahmoud M & Robinson P (2017): Estimating sheep pain level using facial action unit detection. Paper presented to the IEEE International Conference on Automatic Face and Gesture Recognition, Washington, DC. 30 May – 3 June, 2017.
- Viscardi AV, Hunniford M, Lawlis P, Leach M & Turner PV (2017): Development of a Piglet Grimace Scale to Evaluate Piglet Pain Using Facial Expressions Following Castration and Tail Docking: A Pilot Study. Frontiers in Veterinary Science, 4:51. DOI:10.3389/fvets.2017.00051
- Bennett V, Gourkow N & Mills DS (2017): Facial correlates of emotional behaviour in the domestic cat (Felis catus). Behavioural Processes, 141, 342-350.
- McLennan KM, Rebelo CJB, Corke MJ, Holmes MA, Leach MC & Constantino-Casas F (2016): Development of a facial expression scale using footrot and mastitis as models of pain in sheep. Appl. Anim. Behav. Sci., 176, 19–26.
- Di Giminiani P, Brierly VLMH, Scollo A, Gottardo F, Malcolm EM, Edwards SA & Leach MC (2016): The Assessment of Facial Expressions in Piglets Undergoing Tail Docking and Castration: Toward the Development of the Piglet Grimace Scale. Front Vet.Sci., 3, 100.
- Hanson M et al. (2016): Facial expressions and other behavioral responses to pleasant and unpleasant tastes in cats (Felis silvestris catus) Applied Animal Behaviour Science, 181, 129-136.
- Brajon S, Laforest JP, Bergeron R, Tallet C, Hötzel M-J & Devillers N (2015): Persistency of the piglet's reactivity to the handler following a previous positive or negative experience. Applied Animal Behaviour Science, 162, 9-19.
- Briefer EF, Tettamanti F & McElligott AG (2015): Emotions in goats: mapping physiological, behavioural and vocal profiles. Animal Behaviour, 99, 131-143.
- Dalla Costa E, Minero M, Lebelt D, Stucke D, Canali E & Leach MC (2014): Development of the Horse Grimace Scale (HGS) as a Pain Assessment Tool in Horses Undergoing Routine Castration. PLoS ONE doi: 10.1371/journal.pone.0092281
- Proctor HS & Carder G (2014): Can ear postures reliably measure the positive emotional state of cows? Applied Animal Behaviour Science, 161, 20-27. DOI: http://dx.doi.org/10.1016/j.applanim.2014.09.015
- 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. doi:10.1371/journal.pone.0044437
- Leach MC, Klaus K, Miller AL, Scotto di Perrotolo M, Sotocinal SG & Flecknell PA (2012): The Assessment of Post-Vasectomy Pain in Mice Using Behaviour and the Mouse Grimace Scale. PLoS ONE 7(4): e35656. doi:10.1371/journal.pone.0035656
- Leach MC, Coulter CA, Richardson CA & Flecknell PA (2011): Are We Looking in the Wrong Place? Implications for Behavioural-Based Pain Assessment in Rabbits (Oryctolagus cuniculi) and Beyond? PLoS ONE 6(3): e13347. https://doi.org/10.1371/journal.pone.0013347.
- Sotocinal SG, Sorge RE, Zaloum A, Tuttle AH, Martin LJ, Weiskopf JS, Mapplebeck JCS, Wei P, Zhan S, Zhang S, McDougall JJ, King OD & Mogil JS (2011): The Rat Grimace Scale: A partially automated method for quantifying pain in the laboratory rat via facial expressions. Mol. Pain DOI:10.1186/1744-8069-7-55.
- Langford DJ, Bailey AL, Chanda ML, Clarke SE, Drummond TE, Echols S, Glick S, Ingrao J, Klassen-Ross T, LaCroix-Fralish ML, Matsumiya L, Sorge RE, Sotocinal SG, Tabaka JM, Wong D, van den Maagdenberg AMJM, Ferrari MD, Craig KD & Mogil JS (2010): Coding of facial expressions of pain in the laboratory mouse. Nature Methods 7, 447-449.
- Schiavenato MJ (2008): Facial expression and pain assessment in the pediatric patient: the primal face of pain. Spec Pediatr Nurs. 13:89-97. doi: 10.1111/j.1744-6155.2008.00140.x.
- Sandem AI, Braastad BO & Boe KE (2002): Eye white may indicate emotional state on a frustration-contentedness axis in dairy cows. Applied Animal Behaviour Science, 79, 1-10.
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