Development of the Horse Grimace Scale (HGS) as a Pain Assessment Tool in Horses Undergoing Routine Castration

Abstract

BackgroundThe assessment of pain is critical for the welfare of horses, in particular when pain is induced by common management procedures such as castration. Existing pain assessment methods have several limitations, which reduce the applicability in everyday life. Assessment of facial expression changes, as a novel means of pain scoring, may offer numerous advantages and overcome some of these limitations. The objective of this study was to develop and validate a standardised pain scale based on facial expressions in horses (Horse Grimace Scale [HGS]).Methodology/Principal FindingsForty stallions were assigned to one of two treatments and all animals underwent routine surgical castration under general anaesthesia. Group A (n = 19) received a single injection of Flunixin immediately before anaesthesia. Group B (n = 21) received Flunixin immediately before anaesthesia and then again, as an oral administration, six hours after the surgery. In addition, six horses were used as anaesthesia controls (C). These animals underwent non-invasive, indolent procedures, received the same treatment as group A, but did not undergo surgical procedures that could be accompanied with surgical pain. Changes in behaviour, composite pain scale (CPS) scores and horse grimace scale (HGS) scores were assessed before and 8-hours post-procedure. Only horses undergoing castration (Groups A and B) showed significantly greater HGS and CPS scores at 8-hours post compared to pre operatively. Further, maintenance behaviours such as explorative behaviour and alertness were also reduced. No difference was observed between the two analgesic treatment groups.ConclusionsThe Horse Grimace Scale potentially offers an effective and reliable method of assessing pain following routine castration in horses. However, auxiliary studies are required to evaluate different painful conditions and analgesic schedules.

Development of a facial expression scale using footrot and mastitis as models of pain in sheep

“…These changes in facial expression are similar to those described in other species with respect to pain (Dalla Costa et al, 2014;Keating et al, 2012;Leach et al, 2012;Sotocinal et al, 2011). Importantly, there were no changes in the facial expression of non-lame sheep.…”

“…Ley et al (1995) also found sheep previously diagnosed with footrot were still showing an increased response to mechanical stimulation compared to control sheep three months after they had seemingly recovered. Control sheep were also not scored as zero on day 0 or day 90, a finding observed in other studies using facial expression as a pain scoring system (Dalla Costa et al, 2014;Keating et al, 2012). There are several possible explanations for this.…”

“…Footrot was used as our pain model following previous research showing the link between lameness due to footrot and mechanical hyperalgesia (Ley et al, 1989). We followed methods by Langford et al (2010), Sotocinal et al (2011), Leach et al (2012), Keating et al (2012) and Dalla Costa et al (2014) to develop our scale. Images of sheep on days 0 and days 90 were compared to identify changes in facial expression associated with the presence of the disease and lameness.…”

“…a score of 2 for each of the 5 facial areas). The five observers were also asked to make a global assessment of whether they thought the sheep was in pain or not, based on their own previous experience, as used by Dalla Costa et al (2014) and Keating et al (2012).…”

“…Furthermore, the fluctuating nature of spontaneous pain can mean that smaller, more subtle changes are likely to be missed (Foss et al, 2006). Facial expression scoring systems for pain assessment have been recently developed for use in rodents, rabbits and horses (Dalla Costa et al, 2014;Langford et al, 2010;Leach et al, 2012). Facial expression scoring has shown to be successful in identifying and assessing the severity of pain in animals, with minimal time and training required for observers (Langford et al, 2010;Leach et al, 2012;Sotocinal et al, 2011).…”