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

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From: PLoS ONE(Vol. 9, Issue 3)
Publisher: Public Library of Science
Document Type: Article
Length: 7,298 words
Lexile Measure: 1560L

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Author(s): Emanuela Dalla Costa 1,*, Michela Minero 1, Dirk Lebelt 2, Diana Stucke 2, Elisabetta Canali 1, Matthew C. Leach 3

Introduction

The recognition and alleviation of pain is critical for the welfare of horses. Although considerable progress has been made in understanding physiology and treatment of pain in animals over the past 20 years, the assessment of pain in horses undergoing management procedures, such as branding, pin firing and castration, remains difficult and frequently suboptimal [1]-[4]. Equine castration is a husbandry practice routinely performed to: avoid undesired mating, facilitate handling, and reduce aggression and other undesirable behaviours. Annually, it is estimated that 240,000 horses are castrated in Europe [5]. Studies in other species demonstrate that animals experience pain and discomfort both acutely and chronically following castration [6], [7]. Despite the limited research in horses, castration has been shown to be associated with some degree of pain that can persist for several days and, therefore, requires adequate analgesic treatment [2]-[4], [8]. Price et al. [1] reported that only 36.9% of horses received analgesics for post operative pain, with one perioperative administration of Flunixin appearing to be one of the most common analgesic procedure provided following castration [9]: one possible explanation for this is the difficulty in assessing and quantifying pain in this species [2], [10]. For example, even though castration of horses is a common procedure, no gold standard for pain assessment is available to date. As in other animal species, pain in horses is difficult to assess because of their inability to communicate with humans in a meaningful manner. This could be further compounded by horses potentially suppressing the exhibition of obvious signs of pain in the presence of possible predators (i.e. humans) as is suggested with other prey species. Several behaviour-based assessments of pain in horses already exist [11]-[17]. The Post Abdominal Surgery Pain Assessment Scale (PASPAS) is a multidimensional scale that can be used to quantify pain after laparotomy [14]. The Composite Pain Scale (CPS) focuses on the presence of pain-related behaviours and the change in the frequency of normal behaviour patterns and physiological parameters [16]and has been successfully applied following both surgery (e.g. castration), injury and disease (e.g. laminitis, colic) [16], [17]. However, behaviour-based assessments of pain are not without limitations that constrain their routine application. These include the need for trained and experienced observers [8], [16], [17], prolonged observation periods [18], particularly in conditions inducing only mild pain, and the palpation of the painful area in some cases [14], [16], [17]. Furthermore, many of the pain related behaviours described so far have been identified in response to what are perceived to be severely painful conditions (e.g. colic, laminitis [14], [16]), rather than those that are perceived to be mildly to moderately painful conditions (e.g. identification procedures [19]). Recently, a new approach to pain assessment has been developed in rodents and rabbits utilising the assessment of facial expressions [20]-[23]. Facial expressions are commonly used to assess pain and other emotional states in humans, particularly in those...

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Gale Document Number: GALE|A478758691