Coding and quantification of a facial expression for pain in lambs

Abstract

Facial expressions are routinely used to assess pain in humans, particularly those who are non-verbal. Recently, there has been an interest in developing coding systems for facial grimacing in non-human animals, such as rodents, rabbits, horses and sheep. The aims of this preliminary study were to: 1. Qualitatively identify facial feature changes in lambs experiencing pain as a result of tail-docking and compile these changes to create a Lamb Grimace Scale (LGS); 2. Determine whether human observers can use the LGS to differentiate tail-docked lambs from control lambs and differentiate lambs before and after docking; 3. Determine whether changes in facial action units of the LGS can be objectively quantified in lambs before and after docking; 4. Evaluate effects of restraint of lambs on observers' perceptions of pain using the LGS and on quantitative measures of facial action units. By comparing images of lambs before (no pain) and after (pain) tail-docking, the LGS was devised in consultation with scientists experienced in assessing facial expression in other species. The LGS consists of five facial action units: Orbital Tightening, Mouth Features, Nose Features, Cheek Flattening and Ear Posture. The aims of the study were addressed in two experiments. In Experiment I, still images of the faces of restrained lambs were taken from video footage before and after tail-docking (n=4) or sham tail-docking (n=3). These images were scored by a group of five naïve human observers using the LGS. Because lambs were restrained for the duration of the experiment, Ear Posture was not scored. The scores for the images were averaged to provide one value per feature per period and then scores for the four LGS action units were averaged to give one LGS score per lamb per period. In Experiment II, still images of the faces nine lambs were taken before and after tail-docking. Stills were taken when lambs were restrained and unrestrained in each period. A different group of five human observers scored the images from Experiment II. Changes in facial action units were also quantified objectively by a researcher using image measurement software. In both experiments LGS scores were analyzed using a linear MIXED model to evaluate the effects of tail docking on observers' perception of facial expression changes. Kendall's Index of Concordance was used to measure reliability among observers. In Experiment I, human observers were able to use the LGS to differentiate docked lambs from control lambs. LGS scores significantly increased from before to after treatment in docked lambs but not control lambs. In Experiment II there was a significant increase in LGS scores after docking. This was coupled with changes in other validated indicators of pain after docking in the form of pain-related behaviour. Only two components, Mouth Features and Orbital Tightening, showed significant quantitative changes after docking. The direction of these changes agree with the description of these facial action units in the LGS. Restraint affected people's perc...

The Sheep Grimace Scale as an indicator of post-operative distress and pain in laboratory sheep

“…In comparison to the SGS the SPFES comprises more facial expression areas but matches orbital tightening and ear position, which are despite species-specific differences, common parameters for grimace scaling [27]. In line with the recently published Lamb Grimace Scale (LGS) as an indicator for pain in on-farm lambs after tail docking [14] SPFES and SGS are valid and reliable methods for the detection of pain in sheep. However, it is still unclear whether facial expressions change due to other dimensions of severity like stress or suffering, which are likewise related to pain.…”

“…Langford et al were the first who developed a behavioural coding system based on facial expressions to detect signs of pain in laboratory mice, the Mouse Grimace Scale (MGS) [8]. Following to this, grimace scales for laboratory rats [9] and laboratory rabbits [10] were developed, for domestic cats [11] as well as for farm animals like horses [12], sheep [13] and lambs [14]. Moreover, facial expressions as an indicator for pain are generally applied to assess pain or other emotional states in humans [15].…”

Development of a Piglet Grimace Scale to Evaluate Piglet Pain Using Facial Expressions Following Castration and Tail Docking: A Pilot Study

“…While additional work is needed on a larger scale to further validate the PGS and confirm the lack of treatment effects, there have been grimace scales developed using less animals. The Lamb Grimace Scale was developed with 16 animals, although the authors do acknowledge that the results should be interpreted with caution due to these low numbers (6). Another study limitation is not having a strong behavioral baseline to compare to post-procedure behaviors.…”

A Review of Pain Assessment in Pigs

“…In an eye-tracking study of pain behavior in rabbits, it was found that observers focused on the rabbits’ facial features rather than other body areas (irrespective of the observer’s experience) (191). A facial grimace scale was first created for laboratory mice (192), and others have since been created for rats (193), rabbits (194), horses (195), and sheep (196, 197). A Piglet Grimace Scale (PGS) has been developed by experienced observers, who identified several facial action units (FAUs) from images of piglets pre- and post-tail docking and castration (198).…”