A Review of Methods for Detecting Soreness in Horses (2021) / Chapter Skim
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3 New and Emerging Methods, Approaches, and Technologies for Detecting Pain and Its Causes
3 New and Emerging Methods, Approaches, and Technologies for Detecting Pain and Its Causes
Pages 46-73
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From page 46... ...
3 New and Emerging Methods, Approaches, and Technologies for Detecting Pain and Its Causes This chapter addresses the committee's task to identify potential new and emerging methods, approaches, and technologies for detecting hoof and pastern pain and its causes (see Chapter 1, Box 1‐3 for the full statement of task) . This chapter begins with a discussion of factors that affect pain perception and the expression of pain. This is followed by a review of pain detection methods and technologies based on horse behavior and physiological parameters and a discussion of how these methods could be used to improve the detection of soreness in horses during inspections for compliance with the Horse Protection Act (HPA)
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From page 47... ...
New and Emerging Methods, Approaches, and Technologies for Detecting Pain and Its Causes Context and Environment Situational factors can facilitate or inhibit pain expression and thus contribute to scoring and decision errors during an evaluation for pain. The modulation of pain behavior by environmental stressors, distrac‐ tions, other sources of pain, and habituation is discussed below. Stressors Pain and stress are closely related but operationally distinct constructs. Pain is one type of stress that threatens homeostasis, but not every stressor is painful. Behavioral responses to pain may be similar to and confounded with responses to other causes of distress (Rietmann et al., 2004) . To accurately assess pain and avoid confounding pain and stress responses, pain assessment procedures are typically con‐ ducted in an environment with as few extraneous stressors as possible. For example, in scoring a horse's facial expression of pain using the Horse Grimace Scale (HGS)
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From page 48... ...
A Review of Methods for Detecting Soreness in Horses startled by an umbrella opening (the fear condition) trended to score higher on two of six facial indicators, "ears held stiffly backward" and "prominent chewing muscles." On the basis of these findings the re‐ searchers concluded that the assessment tool was a specific indicator of pain. Further discriminant vali‐ dation research of this sort is needed to distinguish pain from other sources of stress in horses. Distractions Horses are inspected for violations of the Horse Protection Regulations at show grounds which have a wide range of environmental distractions, including other horses, exhibitors and spectators, and noises. To reduce distractions, 9 C.F. R. § 11.5(a)
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From page 49... ...
New and Emerging Methods, Approaches, and Technologies for Detecting Pain and Its Causes whips, cigarette smoke, or other actions or paraphernalia are used to distract a horse during examination. Distractions created by horse custodians can contribute to unexplained variance in pain assessment during an inspection and across inspectors. The committee's observation of 61 inspection videos revealed that many exhibitors adhered to Horse Protection Regulations when holding a horse for inspection, but others did not. Horse custodians inadvertently or intentionally held reins closer than 18 inches from the bit shank, touched the horse or the bit, held the reins taut (in some cases above the level of the horse's mouth) , jiggled or jerked on the reins, and stood in front of the horse in a dominant stance. The custodian may have been trying to control or correct an unruly horse, but these distractions can draw the horse's attention away from the digital palpation; a shift in attention has been shown to suppress pain expression (Hoegh et al., 2019; Torcivia and McDonnell, 2020)
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From page 50... ...
A Review of Methods for Detecting Soreness in Horses generally have high thresholds that are only activated by intense stimuli, but tissue injury and peripheral sensitization result in a decreased pain threshold. Thus, digital palpation of a painful area of the pastern could elicit a withdrawal response over a broad area. Individual Differences Horses differ in their sensitivity and response to pain due to differences in genetics, personality, past experiences, and training history. Individual differences result in variations between horses and can help explain why some sored horses, as determined by physical evidence such as a violation of the scar rule or inflammation that is apparent with thermography, may not display pain behaviors. Individual differences in sensitivity, coping style, and training history and their potential effect on pain behavior are described below. Pain Sensitivity Some individuals are inherently more responsive to pain induced by a stimulus than others because of genetically based differences in nociceptor sensitivity and activity. Previous painful insults can also have long‐lasting effects on nociceptor sensitivity. Research on the development of chronic pain has provided information about the neuroplasticity of pain. For example, repeated injury can exacerbate a painful stim‐ ulus and experience through an increase in the number and activity of pain receptors (Woolf, 1989) . This can lead to hyperalgesic priming, which is an increased sensitivity to subthreshold stimuli, and in extreme cases to allodynia, where pain is caused by a stimulus that does not normally elicit pain, such as the light touch of clothes on sunburned skin (Latremoliere and Woolf, 2009)
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From page 51... ...
New and Emerging Methods, Approaches, and Technologies for Detecting Pain and Its Causes training history. In one study, compliance, as measured by latency to cross a tarp or walk through stream‐ ers, did not correlate with physiological indicators of stress, including heart rate variability, infrared eye temperature, and core body temperature (Squibb et al., 2018) . The researchers hypothesized that com‐ pliance (such as standing still and following)
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From page 52... ...
A Review of Methods for Detecting Soreness in Horses with laminitis (van Loon and Van Dierendonck, 2019) . In addition, clinical scales are expected to be used by a large number of raters; inter‐rater agreement, and thus the validity of the assessment method, is ensured through standardized training and consistent application across raters. Uncontrolled extraneous factors can also introduce error into the assessment. Some behaviors are robust against, and others more easily modulated by, extraneous variables. Pain behavior can be inhibited or facilitated by extraneous variables. Factors that influence variability in the expression of pain are discussed below. As Sator‐Katzenschlager (2014)
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From page 53... ...
New and Emerging Methods, Approaches, and Technologies for Detecting Pain and Its Causes BEHAVIORAL ASSESSMENT OF PAIN The goal of inspections is, as described in Chapter 1 of this report, to examine a horse to determine compliance with or violation of the HPA. Designated qualified persons (DQPs) and, less often, veterinary medical officers (VMOs)
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From page 54... ...
A Review of Methods for Detecting Soreness in Horses the tools' clinical application (de Grauw and van Loon, 2016) . Pain assessment conducted in the field tends to employ scales that are simpler, take less time to complete and score, and yield rapid results. These features facilitate diagnosis and treatment in real‐life conditions and when time is limited. The development of clinical scales for assessing pain in animals lags behind, but parallels, the develop‐ ment of these scales in humans. Pain assessment in infants (Riddell et al., 2013)
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From page 55... ...
New and Emerging Methods, Approaches, and Technologies for Detecting Pain and Its Causes TABLE 3‐1 Score Sheet for the EQUUS‐COMPASS Composite Pain Scale Data Categories Score Physiological data Heart rate 24–44 beats/min 0 45–52 beats/min 1 53–60 beats/min 2 >60 beats/min 3 Respiratory rate 8–13 breaths/min 0 14–16 breaths/min 1 17–18 breaths/min 2 >18 breaths/min 3 Rectal temperature 36.9–38.5°C 0 36.4–36.9°C or 38.5–39.0°C 1 35.9–36.4°C or 39.0–39.5°C 2 35.4–35.9°C or 39.5–40.0°C 3 Digestive sounds Normal motility 0 Decreased motility 1 No motility 2 Hypermotility or steelband 3 Behavior Posture (weight distribution, Stands quietly, normal walk 0 comfort) Occasional weight shift, slight muscle tremors 1 Non‐weight bearing, abnormal weight distribution 2 Analgesic posture (attempts to urinate)
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From page 56... ...
A Review of Methods for Detecting Soreness in Horses TABLE 3‐1 Score Sheet for the EQUUS‐COMPASS Composite Pain Scale Data Categories Score Head movements No evidence of discomfort, head straight ahead for the most part 0 Intermittent head movements laterally/vertically, occasional looking at flank 1 (1–2 times/5 min) , lip curling (1–2 times/5 min)
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New and Emerging Methods, Approaches, and Technologies for Detecting Pain and Its Causes TABLE 3‐2 Obel Laminitis Grades for Rating a Horse's Withdrawal from Pressure/Palpation of Localized Area Grade Behavioral Description Normal Horse appears sound Obel grade I At rest, the horse shifts its weight between the forelimbs; the horse is sound at the walk, but the gait is stilted at the trot in a straight line and on turning Obel grade II The gait is stilted at the walk and the horse turns with great difficulty, but one forelimb can be lifted Obel grade III The horse is reluctant to walk, and one forelimb can only be lifted with great difficulty Obel grade IV Horses express marked reluctance or absolute refusal to move SOURCE: Adapted from Meier et al. (2019) . inspectors evaluate a horse's gait while it is walking on a straight line and turning in accordance with 9 C.F.R. § 11.21 9(a)
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From page 58... ...
A Review of Methods for Detecting Soreness in Horses TABLE 3‐3 Facial Features of Horses in Pain Pain Expression Facial Features Gleerup et al. (2015) Dalla Costa et al. (2014)
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From page 59... ...
New and Emerging Methods, Approaches, and Technologies for Detecting Pain and Its Causes FIGURE 3‐1 Horse Grimace Scale. Score is the sum of six features, rated as not present (0) , moderately present (1)
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From page 60... ...
A Review of Methods for Detecting Soreness in Horses The CPS is a multifactorial scale that includes physiological measures, spontaneous behaviors, and evoked responses to stimuli (Table 3‐1) . Each of the 13 items is assigned a score from 0 to 3, giving a total pain score ranging from 0 (no signs of pain)
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From page 61... ...
New and Emerging Methods, Approaches, and Technologies for Detecting Pain and Its Causes Finding 3‐6: DQPs are directed to observe the horse for responses to pain during the inspection process in 9 C.F.R. § 11.21. Some information about behavioral indicators of pain appear in the APHIS training material for DQPs. However, the training material lists "abnormal reactions of the eye, ears, and head in response to palpation." The term "abnormal" is unnecessarily vague, given that specific facial expressions indicative of pain have been described in clinical research literature. Finding 3‐7: Pain can be detected accurately and consistently when it is assessed using physical, physio‐ logical, and behavioral parameters that are based on validated clinical scales. Finding 3‐8: Clinical research in horses under veterinary care for laminitis and orthopedic injuries has con‐ firmed that pain assessment using the withdrawal response to palpation is an accurate and reliable method for identifying pain, with very high agreement between raters. TABLE 3‐4 Score Sheet for the Equine Utrecht University Scale for Facial Assessment of Pain (EQUUS‐FAP) Scale Data Categories Score Head Normal head movement; interested in environment 0 Less movement than normal 1 No Movement 2 Eyelids Opened eyelids; sclera can be seen in case of eye/head movement 0 More opened than normal or tightening of eyelids. An edge of the sclera can be seen for 1 50% of the time Obviously more opened eyes or obvious tightening of eyelids. Sclera can be seen more 2 than 50% of the time Focus Focused on environment 0 Less focused on environment 1 Not focused on environment 2 Nostrils Relaxed 0 A bit more opened than normal 1 Obviously more opened than normal; nostril flaring and possibly audible breathing 2 Corners mouth/lips Relaxed 0 Lifted a bit 1 Obviously lifted 2 Muscle tone head No fasciculations 0 Mild fasciculations 1 Obvious fasciculations 2 Flehmen and/or yawn Absent 0 Present 2 Teeth grinding and/or Absent 0 moaning Present 2 Ears Position: Orientation toward sound; clear response with both ears or ear closest to source 0 Delayed or reduced response to sound Position: backwards or no response to sound 1 2 Total 18 SOURCE: van Loon and Van Dierendonck (2017, supplementary table S1)
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From page 62... ...
A Review of Methods for Detecting Soreness in Horses FIGURE 3‐3 Photographs captured from videotaped standing inspections by designated qualified persons before (left) and during (right)
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From page 63... ...
New and Emerging Methods, Approaches, and Technologies for Detecting Pain and Its Causes TABLE 3‐5 Behavioral Assessment Scales Basis, Pros, and Cons Scale (author) Assessment Basis Pros Cons Composite Pain Scale (Bussieres Identification of flexor NWR is reliably elicited by et al., 2008)
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From page 64... ...
A Review of Methods for Detecting Soreness in Horses TABLE 3‐5 Continued Scale (author) Assessment Basis Pros Cons Equine pain face (Gleerup et al., Burning pain induced Experimental study with Inter‐rater reliability, sensitivity, 2018)
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From page 65... ...
New and Emerging Methods, Approaches, and Technologies for Detecting Pain and Its Causes inconsistent application of technique than from the validity of the pain assessment procedure itself. An‐ other factor might be conflict of interest, which the USDA OIG 2010 audit found was an influence on how DQPs conducted inspections. PHYSIOLOGICAL ASSESSMENT OF PAIN Physiological measurements have been used extensively in assessing pain in horses and humans, both in clinical practice and in applied research. The factors that are measured include, but are not limited to, heart rate and heart rate variability, respiratory rate, body temperature, ocular temperature, blood pressure, and various endogenous substances such as beta‐endorphins, cortisol, serotonin, dopamine, substance P, and oxytocin. This section includes a discussion of physiological parameters that are used to assess or indicate pain as well as of the biomarkers and noninvasive techniques that have been explored for their utility in pain and stress assessment. To the committee's knowledge, these parameters are not currently included in the TWH inspection process and may warrant further investigation for such a pur‐ pose. Physiological Parameters as Indicators of Pain and Stress The advantages of physiological values over other methods to assess pain are that they are objective, are noninvasive, and can be measured relatively easily and repeatably. Heart rate, respiratory rate, and temperature are routinely measured during a physical exam; endogenous substances can be measured from blood samples. Heart rate variability, ocular temperature, and blood pressure measurements require specialized equipment and are therefore not routinely measured during a physical exam, but they are frequently included as part of research on the physiology of pain and stress. The major disadvantages of these measurements are: (1) they have been shown to have low specificity for pain (Rietmann et al., 2004)
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From page 66... ...
A Review of Methods for Detecting Soreness in Horses cortisol levels are used as a biomarker for the stress response (Coetzee et al., 2008) . Interestingly, vocali‐ zation by calves during the procedure was significantly correlated with levels of SP but not with cortisol levels. In another study, serum SP was found to be higher in dogs with fractures or medial patella luxation than in healthy controls that underwent the same clinical procedures (Yoon et al., 2019)
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From page 67... ...
New and Emerging Methods, Approaches, and Technologies for Detecting Pain and Its Causes Finding 3‐13: Ocular thermography has been shown to discriminate between pain and distress in calves undergoing castration. It has also been used to quantify stress in horses during athletic performance and in horses that wear tight nosebands. Conclusion 3‐7: The show environment and other conditions during inspections may cause physiological changes in horses that mirror those seen in pain, thus limiting utility of physiological parameters to help detect if a horse is experiencing soreness. Conclusion 3‐8: Although often included as predictors in composite pain scales to bolster their validity and reliability, physiological parameters are not meant to be used in isolation to detect pain, but instead should be integrated with other measures in a multimodal approach. Conclusion 3‐9: The potential of ocular thermography to help differentiate between pain and stress in TWHs and its utility in detecting soreness warrant further investigation. CLINICAL ASSESSMENT OF PAIN Pain recognition in horses is complex and typically involves a multimodal approach including obser‐ vational and objective measures, visual inspection for signs of trauma and an antalgic stance, changes in facial expressions captured in composite pain scales (see section on Behavioral Assessment of Pain in this chapter) , physiological parameters (see section on Physiological Assessment of Pain in this chapter)
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From page 68... ...
A Review of Methods for Detecting Soreness in Horses pain behavior makes remote observation via video recordings ideal, but this is not possible at horse shows. Interactions with handlers, spectators, and other horses and simply being in the foreign environment of an equestrian competition will all alter a horse's behavior and potentially mask signs of pain. A visual inspection for signs of pain should include an assessment of general demeanor and posture. Signs of pain are nonspecific and may include (but are not limited to) excessive quietness or restlessness, low head carriage, weight shifting, pointing a front limb or resting a hind limb, standing hunched over or camped out, and looking at a painful area. Other signs may include bruxism (grinding of teeth)
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From page 69... ...
New and Emerging Methods, Approaches, and Technologies for Detecting Pain and Its Causes Gait Analysis -- Kinematics, Kinetics Another key factor in determining a horse's fitness to compete safely is the confirmation of the ab‐ sence of lameness, or pain causing an irregular gait (Adams, 2015) . In most official equestrian competi‐ tions, including racing, this is done by careful inspection of the horse at trot in a straight line, on a loose lead, and in hand and by observing for asymmetric head, limb, and pelvic movements. Veterinarians use subjective lameness grades, most commonly the five‐point American Association of Equine Practitioners (AAEP)
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From page 70... ...
A Review of Methods for Detecting Soreness in Horses Recommendation 3‐2: To help improve accuracy of soreness detection, the horse inspector should ensure that custodians are following guidelines that prohibit stewarding while the horse is being inspected, and should closely monitor horse custodians for violations. Recommendation 3‐3: Pain assessment using facial expressions is a new area of research, and scientific investigations of these methods have not been performed in TWHs. However, evidence supports the use of facial expressions of pain as supplemental information, if video is available to review or if a second inspector is present. Recommendation 3‐4: To improve consistency across inspectors, science‐based information about be‐ havioral and facial indicators of pain in horses should be incorporated into inspectors' training. Recommendation 3‐5: Research is needed to study validity and potential utility of using facial grimace for assessing pain in TWHs and to distinguish pain from other sources of distress. To accomplish this, re‐ searchers could, under show conditions, apply new clinical pain assessment technologies and score the horse's behavior and facial expressions during the inspection. Facial expressions of pain are expected to correlate with findings from other currently used methods to detect soreness, such as palpation. For this purpose, it is important to capture the horse's head in the inspection videos. Recommendation 3‐6: The decision to disqualify a horse due to soreness should be driven by an experi‐ enced veterinarian, such as a VMO, and should be based on diagnosis of local pain detected on palpation but should also include a more thorough gait or lameness assessment to identify other sources of pain. Signs of pain that should be observed include excessive quietness or restlessness, low head carriage, weight shifting, pointing a front limb or resting a hind limb, standing hunched over or camped out and looking at a painful area, bruxism, sweating, and muscle fasciculations. REFERENCES Adams, S. B. 2015. The lameness examination in horses. https://www.merckvetmanual.com/musculoskeletal‐ system/lameness‐in‐horses/the‐lameness‐examination‐in‐horses (accessed July 31, 2020) . Allweiler, S. 2020. Recognizing and assessing pain in animals. https://www.merckvetmanual.com/special‐pet‐ topics/pain‐management/recognizing‐and‐assessing‐pain‐in‐animals (accessed July 20, 2020)
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From page 71... ...
New and Emerging Methods, Approaches, and Technologies for Detecting Pain and Its Causes Dalla Costa, E., D. Stucke, F. Dai, M. Minero, M. C. Leach, and D. Lebelt. 2016. Using the Horse Grimace Scale (HGS) to assess pain associated with acute laminitis in horses (Equus caballus)
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From page 72... ...
A Review of Methods for Detecting Soreness in Horses Kennedy, D. L., H. I. Kemp, D. Ridout, D. Yarnitsky, and A. S. Rice. 2016. Reliability of conditioned pain modulation: A systematic review. Pain 157(11) :2410–2419. Koolhaas, J. M., and C. G. Van Reenen. 2016. Interaction between coping style/personality, stress, and welfare: Relevance for domestic farm animals. Journal of Animal Science 94:2284–2296. Koolhaas, J. M., S. M. Korte, S. F. De Boer, B. J. Van Der Vegt, C. G. Van Reenen, H. Hopster, I. C. De Jong, M. A. W. Ruis, and H. J. Blokhuis. 1999. Coping styles in animals: Current status in behavior and stress‐physiology. Neuroscience & Biobehavioral Reviews 23(7)
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From page 73... ...
New and Emerging Methods, Approaches, and Technologies for Detecting Pain and Its Causes Roepstorff, L., A. Egenvall, M. Rhodin, A. Byström, C. Johnston, P. R. Van Weeren, and M. Weishaupt. 2009. Kinetics and kinematics of the horse comparing left and right rising trot. Equine Veterinary Journal 41(3) :292–296. Sator‐Katzenschlager, S. 2014. Pain and neuroplasticity. Revista Médica Clínica Las Condes 25(4)
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