Grimace scales

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 the mouse (Langford et al., 2010; Leach et al., 2012), rat (Sotocinal et al., 2011), rabbit (Keating et al., 2012), horse (Dalla Costa et al., 2014) and sheep (Häger et al., Lu et al., McLennan et al., 2016 and McLennan & Mahmoud, 2019). Researchers are working on similar scales for the rhesus monkey and pig (Di Giminiani et al., 2016).

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.


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. 

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

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.

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

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

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.

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

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.

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. 2016, 176, 19–26.

McLennan K & Mahmoud M (2019): Development of an Automated Pain Expression Detection System for Sheep (Oves Aries). Animals, 9, 196

Proctor HS & Carder G (2014): Can ear postures reliably measure the positive emotional state of cows? Applied Animal Behaviour Science, 161, 20-27. DOI:

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.

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.

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.

McLennan et al., (2019): Conceptual and methodological issues relating to pain assessment in mammals: The development and utilisation of pain facial expression scales

Zhang et al. (2019): Influence of Rater Training on Inter- and Intra-rater Reliability When Using the Rat Grimace Scale

Facial expressions and other behavioral responses to pleasant and unpleasant tastes in cats (Felis silvestris catus)

This page was updated on 28 November 2019

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