A Review of Methods for Detecting Soreness in Horses (2021) / Chapter Skim
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Summary The Tennessee walking horse (TWH) , a breed that originated in Tennessee more than 100 years ago, is known for its ability to navigate rough terrains with ease, its smooth and easy gaits, and mild and obe‐ dient temperament. TWHs are also particularly popular in horse show competitions owing to their unique four‐beat running walk and flashy movement. TWH competitions fall into two basic categories: flat‐shod and performance. Flat‐shod horses wear traditional horseshoes and are judged on brilliance and show presence while still being well mannered, balanced, and manageable. Performance horses are fitted with tall, heavy stacks of pads to accentuate the gait they are best known for, referred to as the "big lick," which draws people to horse shows and is rewarded by horse show judges. While some trainers of TWHs believe that the big lick can be achieved with hard work, training, and patience, there are also trainers who resort to soring, a practice that began in the early 1950s for training TWHs to exaggerate their gait in less time. Soring involves the application of chemical irritants and friction to make the horse's forelegs sore, which causes the horse, when it makes contact with the ground, to flex its forelimbs exaggeratedly and snap them forward -- producing the big lick. Because soring gave horses a competitive advantage, the practice became widespread in the 1960s. Increased public awareness of soring and the resulting backlash prompted the state of Tennessee to enact anti‐soring legislation in 1950, which was mostly disregarded by the industry and ultimately not enforced. In 1970 the U.S. Congress declared the practice of soring cruel and inhumane and passed the Horse Protection Act (HPA, 15 U.S.C. §§ 1821‐1831)
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A Review of Methods for Detecting Soreness in Horses required to be veterinarians. To ensure that horses are disqualified when soreness is detected or when other HPA violations4 are found and that proper penalties were imposed by the HIO for noncompliance with rules set forth in the HIO rule book,5 APHIS reviews reports written by show management, HIOs, and DQPs and conducts audits of records maintained by certified DQP programs. VMOs also attend selected horse shows and sales to assess HIOs' inspection procedures and DQPs' performance. VMOs conduct ad‐ ditional unannounced inspections at only very few shows. According to a 2010 audit by the USDA Office of the Inspector General (OIG) , in FY 2007, with a $497,000 budget for HPA enforcement, APHIS was able to send VMOs to only 30 (6 percent)
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Summary BOX S‐1 Statement of Task The National Academies of Sciences, Engineering, and Medicine will convene an ad hoc committee of equine veterinarians and experts with relevant experience and appropriate professional certifications or academic de‐ grees to review the scientific and veterinary medical literature on hoof and pastern pain and skin/tissue changes on the pastern of horses and evaluate methods used to identify soreness in horses (as defined in the Horse Pro‐ tection Acta and the implementing regulations) for their scientific validity and reliability. In the course of its study, the committee will: examine what is known about the quality and consistency of available methods to identify soreness in horses identify potential new and emerging methods, approaches, and technologies for detecting hoof and pas‐ tern pain and its causes identify research and technology needs to improve the reliability of methods to detect soreness In a consensus report, the committee will describe its conclusions about the validity and reliability of methods and provide recommendations to improve the efficacy and consistency of approaches to identifying soreness. The report will also review the Horse Protection Act regulations, including the "scar rule" found at 9 C.F.R. § 11.3, and identify changes that would be necessary to implement the findings of the study. a Sore when used to describe a horse means: (1)
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A Review of Methods for Detecting Soreness in Horses examinations be done thoroughly using proper techniques and used in conjunction with other diagnostic technologies, tools, and techniques. Recommendation 2‐1: In line with the USDA OIG's recommendation in 2010, the committee strongly rec‐ ommends that use of DQPs for inspections be discontinued and that only veterinarians, preferably with equine experience, be allowed to examine horses, as is done in other equine competitions. Recommendation 2‐2: If the limited budget for HPA enforcement necessitates continued use of third‐ party inspectors, they should be veterinarians or equine industry professionals who are screened for po‐ tential conflicts of interest and are trained to inspect by APHIS, not by HIOs. This is in line with the rule proposed by APHIS in 2016 and finalized in 2017 but not yet implemented. Training should be done by experienced equine veterinarians, and strict competency evaluations should be conducted to assess the skills and knowledge of trainees before they are given license to inspect horses. Consequences for per‐ forming a substandard examination should be strictly enforced, and reports of substandard performance and letters of admonishment should come from APHIS, not HIOs. Recommendation 2‐3: APHIS should adhere to 9 C.F.R. § 11.4(h)
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Summary doubt on the ability of VMOs to detect pain or other abnormalities and may negatively affect the VMOs' ability to make appropriate judgments. Conclusion 2‐5: The basis of all examinations for pain and lameness is observation and palpation, which are an integral part of determining whether pain is altering gait in a TWH. The strict requirements of fol‐ lowing a specified pattern and using only the pad of the thumb with no more pressure than it takes to blanch the thumbnail limit the ability of palpation to detect the presence of limb sensitivity. The require‐ ment that two VMOs must make exactly the same findings (i.e., sensitive on the lateral pastern but not bulbs of heels or medial pastern) does not consider changes that may occur over time between examina‐ tions, how the horse may respond to repeated palpation, or how the presence of foreign substances either parenterally or topically may influence findings over time. Recommendation 2‐4: In digital palpation of distal limbs, the extent of digital pressure need not be pre‐ scribed, provided that experienced equine veterinarians are performing the inspections. Use of palpation from the carpus distally to determine the presence or absence of limb sensitivity is well established in other equine competitions. Horses with limb sensitivity in these competitions must be withdrawn for the welfare of the horse and safety of the rider. Recommendation 2‐5: Owing to physiological changes that occur after repeated stimulation of a painful area, inspection protocols should be based on current knowledge of pain perception and should exclude the requirement that horses be repeatedly sore in a specific area to be disqualified. Testing to Detect Substances that Cause or Mask Soreness Finding 2‐6: Budgetary constraints limit swabbing and testing by APHIS for prohibited substances that cause soreness or that can mask soreness. Conclusion 2‐6: Testing of swabs is an effective method to determine if foreign substances have been applied to the limb of horses to cause soreness or to mask soreness. Recommendation 2‐6: To detect prohibited substances, swabs should be done on a random sampling of horses or on horses that the VMO identifies as suspect from observations made on the grounds of the horse show. Thermography Finding 2‐7: Thermography, an imaging technique that veterinarians use to detect inflammation and that was used in HPA enforcement in the past, is currently not being used in detecting soreness during horse inspections. Conclusion 2‐7: Thermographic cameras are an objective tool for recognizing alterations in blood flow to the limbs of horses, which is indicative of inflammation. Thermography can be a screening tool in the inspection process and can provide supporting evidence of soreness, which may increase the efficiency and reliability of the inspection process. Recommendation 2‐7: Thermography should be reinstituted in the inspection of TWHs. 5
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A Review of Methods for Detecting Soreness in Horses Blood Testing to Detect Medications Finding 2‐8: Blood sampling to test for prohibited medications and medications conditionally permitted but given above therapeutic levels is common in equestrian competitions around the world to protect horse welfare and to ensure fairness in competition. Testing is done according to medication rules and guidelines set by a regulatory body based on data on how the use or overuse of these medications can adversely affect the horse or alter its performance. Regulatory bodies, such as the United States Eques‐ trian Federation (USEF) and International Federation for Equestrian Sports require identification of horses by microchip for identity verification, information sharing, and record keeping. Finding 2‐9: Medications given to TWHs are the same as the medications administered to other competi‐ tion horses and include all of the opioids, sedatives, local anesthetics, and nonsteroidal anti‐inflammatory drugs (NSAIDs)
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Summary Finding 3‐5: Observation of 61 inspection videos revealed numerous incidents of stewarding during the standing inspection that were not dealt with by the inspector. Stewarding may have simply been out of habit or to prevent or control the horse's restless behavior. Examples of stewarding included holding the reins closer than 18 inches from the bit, often just below or on the shank. In some cases, the horse was restrained with constant tension, often with the reins held in an upward direction, or the reins were pulled sharply. These restraint tactics create a distraction during the palpation procedure and can induce pain in the oral cavity, and they violate Horse Protection Regulations. Conclusion 3‐1: Environmental distractions present during horse inspections can result in the inspector reaching inaccurate conclusions regarding soreness. Distractions and stressors can inhibit a horse's sensi‐ tivity to and expression of pain, such that detection of soreness would be missed, or a horse's reaction to distractions could be incorrectly attributed to pain. Moreover, when more than one inspector examines the horse, its behavior may differ between the two inspections if the number and type of distractions and stressors at that location and time also differ. Conclusion 3‐2: Pain or discomfort can be caused by restraint during an inspection. Some restraint meth‐ ods create acute oral cavity pain that can inhibit limb and hoof pain. How a horse is restrained during an inspection may differ between inspectors and could result in different observations and conclusions about the same horse. Recommendation 3‐1: Designating an inspection area that has as few distractions as possible will reduce the effect of the environment on the horse's response to pain during examination. It is important that inspectors observe the horse's response to the show environment and to restraint before starting the inspection and consider the horse's behavior in the decision‐making process. Recommendation 3‐2: To help improve accuracy of soreness detection, the 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. Behavioral Assessment of Pain 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. Finding 3‐9: Horse Protection Regulations do not include current information about equine pain behavior and its application to clinical practice. Facial grimace scales have long been used in human medicine to assess pain in infants and young children and are currently used in laboratory animal research and veter‐ inary care to assess pain and welfare state. 7
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A Review of Methods for Detecting Soreness in Horses Finding 3‐10: Some horses displayed a facial grimace during standing inspection in the 61 videos provided to the committee. However, the videos also showed that various factors, such as dim lighting, a horse's dark color, and an inspector's body position and direction of gaze while palpating the limb, may prevent a single inspector from simultaneously palpating the forelimb and observing the horse's facial expression. Conclusion 3‐3: A common set of objective criteria grounded in behavioral science, including facial ex‐ pressions indicative of pain, is lacking from inspector training. Thus, an inspector's interpretation of a horse's behavior is subjective, but it can influence a determination of soreness. Conclusion 3‐4: Research is needed to determine the utility of assessing facial expression of pain in TWHs as part of the inspection procedure before use of facial expressions can be proposed as an additional method for detecting soreness. It is important to know if facial grimace can be reliably identified by dif‐ ferent inspectors. It is also important to determine the extent to which the facial expressions of pain cor‐ respond to current evidence of soreness during inspections, such as withdrawal responses to digital pal‐ pation and findings of noncompliance with the scar rule criteria. Conclusion 3‐5: One practical limitation to including facial expressions to assess pain during digital palpa‐ tion is the challenge an inspector might have of simultaneously observing the horse's face and forelimb. Conclusion 3‐6: In clinical research, agreement between raters on horses' responses to digital palpation is consistently high. While agreement may be lower when palpation is carried out in a show environment, differences between inspectors' findings are more likely to result from inadequate training and incon‐ sistent application of technique than from the validity of the pain assessment procedure itself. Another factor might be conflict of interest, which the USDA OIG 2010 audit found was an influence on how DQPs conducted inspections. 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 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. Pain Assessment Using Physiological Parameters Finding 3‐11: Physiological parameters (e.g., heart rate, respiratory rate, body temperature, and blood pressure) have been used extensively to assess pain in horses and humans. They are objective and can be measured easily and repeatably; however, they have low specificity for pain, vary across individuals, and fluctuate between measurements. 8
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Summary Finding 3‐12: Most physiological measures do not discriminate between pain and other sources of auto‐ nomic arousal. Changes in physiological parameters, while indicative of pain, may also be due to physical exertion, excitement, stress, dehydration, hyperthermia, or certain medications. 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 Finding 3‐14: Pressure algometry has been used to determine pain thresholds in TWHs that are not sore. A study6 has shown that TWHs that were not sore responded with a withdrawal reflex only to pressures greater than 10 kg/cm2 (10 times greater than the pressure needed to blanch the thumbnail, which is what APHIS VMOs are prescribed to apply when palpating horses during inspections at TWH shows) . Finding 3‐15: There is a lack of kinetic and kinematic research studies in TWHs that are needed to establish gait characteristics of TWHs that are and are not sore. Conclusion 3‐10: The absence of studies to differentiate pain from stress in TWHs indicates a need for further research. Conclusion 3‐11: Further research is needed on using pressure algometry in TWHs with sore limbs. Kinetic and kinematic research in normal TWHs and those with sore limbs is also needed to establish gait charac‐ teristics in this breed. 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. 6 Haussler, K. K., T. H. Behre, and A. E. Hill. 2008. Mechanical nociceptive thresholds within the pastern region of Tennessee walking horses. Equine Veterinary Journal 40(5)
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A Review of Methods for Detecting Soreness in Horses Review of the Scar Rule Finding 4‐1: Evaluation of skin samples collected from TWHs that were found to be noncompliant with the scar rule indicated variable (moderate to severe) epidermal hyperplasia (clinically evident thickening and roughness or lichenification)
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Summary Conclusion 4‐5: The scar rule language needs to be based on what can accurately be assessed by a gross examination, which ideally would only be performed by an experienced equine practitioner. Recommendation 4‐1: Regardless of why the scar rule was written with limited information and limited expertise in pathological changes in the skin, the committee recommends that the rule be revised. The committee's proposed language is as follows: A trained inspector should examine skin of the front limb of the horse from the knee (carpus) to the hoof with particular attention to skin of pastern and fetlock and the coronary band. All areas of skin from carpus to hoof of both limbs should be free of foreign substances such as dyes, hair fillers, ointments, and other substances designed to camouflage scar rule violations during pre‐ and post‐ show inspections. Detection of previously approved substances such as lubricants during post‐com‐ petition inspection does not constitute a violation. There should be no chemical smell emanating from the skin and no substance present that can be rubbed off onto the hands or a cloth. Skin should be haired with no areas of loss of hair, patchy or diffuse. There can be no swelling, redness, excoria‐ tion, erosions, ulcers, seeping of fluids, or signs of a response to chronic injury such as epidermal thickening or presence of scales. Photo documentation of lesions, identifying information about the horse, and a date should be provided for any horse determined to be or suspected of being in viola‐ tion of the scar rule. 11
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