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 obedient 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), which makes it illegal to exhibit, transport, sell, or auction horses that are known to be sore¹ and authorizes the inspection of horses by U.S. Department of Agriculture (USDA) Animal and Plant Health Inspection Service (APHIS) personnel. However, with funding limited to about $500,000/year, the ability of APHIS to enforce the HPA nationally was limited. In 1976, Congress amended the HPA which then allowed the Secretary of Agriculture to expand the inspection program. The Secretary subsequently created a program that would permit trained third-party individuals (referred to as designated qualified persons, or DQPs) to conduct horse inspections. The DQP program was established by regulations published in the Federal Register in 1979.²

APHIS relies on DQPs, horse industry organizations (HIOs), and veterinary medical officers (VMOs, who are APHIS veterinarians) to inspect horses before they are shown, sold, or exhibited in public. A DQP has authority from an HIO³ to inspect horses or check records for HPA enforcement. After HIOs obtain USDA certification, DQPs are licensed through DQP programs that are administered by HIOs. DQPs are not

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¹ “The Act states that the term ‘sore’ when used to describe a horse means that the horse suffers, or can reasonably be expected to suffer, physical pain or distress, inflammation, or lameness when walking, trotting, or otherwise moving as a result of: an irritating or blistering agent applied, internally or externally, by a person to any limb of a horse; any burn, cut, or laceration inflicted by a person on any limb of a horse; any tack, nail, screw, or chemical agent injected by a person into or used by a person on any limb of a horse; or any other substance or device used by a person on any limb of a horse or a practice that a person has engaged in involving a horse.” Source: USDA APHIS. 2012. Horse Protection Act; requiring horse industry organizations to assess and enforce minimum penalties for violations. Fed. Reg. 77:33607-33619. https://www.federalregister.gov/documents/2012/06/07/2012-13759/horseprotection-act-requiring-horse-industry-organizations-to-assess-and-enforce-minimum-penalties (accessed October 16, 2019).

² APHIS. 2016a. Horse Protection Act and its administration. https://www.aphis.usda.gov/aphis/ourfocus/animalwelfare/hpa/ct_hpa_history_and_administration (accessed February 13, 2020).

³ An HIO is an organization engaged in the showing, exhibition, sale, auction, or registration of 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 additional 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) of the 463 sanctioned shows throughout the country. The OIG audit also found that the DQP program “was not functioning as intended,” noting that DQPs may have conflicts of interest due to their close ties with the industry.

PURPOSE OF THE STUDY AND THE COMMITTEE’S CHARGE

Although VMOs and DQPs use similar methods to inspect horses for soreness, there have been significant disparities between VMO and DQP inspection outcomes. The 2010 USDA OIG audit found that DQPs issue fewer tickets when not being observed by APHIS representatives. There is also a concern within the TWH industry that the determination of soreness is inconsistent between inspectors because the methods themselves may not be reliable. Another focus of debate is the technical merits of the “scar rule” (see Box 1-2 in Chapter 1), which describes lesions on the horse’s pastern and fore pastern that suggest a horse has been subjected to soring.

In July 2017, APHIS and the TWH industry jointly requested the National Academies of Sciences, Engineering, and Medicine (the National Academies) to oversee an independent study to help ensure that HPA inspection protocols, including protocols for compliance with the scar rule, are based on sound scientific principles that can be applied with consistency and objectivity. The study committee’s statement of task is in Box S-1.

To fulfill its charge, the committee reviewed the methods that are currently used by VMOs and DQPs and the methods typically used by equine veterinarians to determine if a horse is experiencing pain. In addition, the committee investigated other methods and technologies that could potentially aid in examining the horse’s limbs for soreness. The committee also reviewed the scar rule of the HPA to determine if the language of the rule is consistent with current findings relative to dermatopathological changes seen in walking horses examined recently versus when the rule was written over 40 years ago.

FINDINGS, CONCLUSIONS, AND RECOMMENDATIONS

Horse Inspections by Designated Qualified Persons and Veterinary Medical Officers

Finding 2-1: At shows covered by the Horse Protection Act (HPA), horse inspections are performed by a designated qualified person (DQP) employed by horse industry organizations (HIOs) or, less often, by a USDA veterinary medical officer (VMO) or, in some instances, by both. These individuals have different backgrounds, training, and experience in detecting pain and inflammation in animals. DQPs are not required to have a veterinary degree, and most are not veterinarians. DQPs receive 10 hours of instruction in examining horses from instructors who are not veterinarians. VMOs attended veterinary school for 4 years, and some have private-practice experience prior to being employed by APHIS. Additionally, DQPs are known to have close ties to the industry and may have conflicts of interest (as pointed out in the 2010 OIG audit).

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⁴ These violations are described in the Horse Protection Regulations in Appendix C of this report.

⁵ HIOs are required to submit rule books to APHIS every year.

Finding 2-2: The current horse inspection process for detecting soreness involves observation of the horse’s movement and posture and palpation of the limbs, which is the gold standard for detecting local pain and inflammation. These examination methods are known to be valid and reliable when performed by veterinarians who are trained and highly experienced in detecting lameness and pain. They are employed to detect lameness, injury, and pain in all breeds of horses that are used in competitions, shows, recreational riding, work, breeding, and teaching.

Conclusion 2-1: Differences in training and experience account for the discrepancies between VMO and DQP inspection results in past years. This discrepancy will continue to affect inspection outcomes if DQPs are not trained adequately and evaluated for competency by experienced equine veterinarians. Conflicts of interest may also influence decisions of DQPs in finding whether a horse is in compliance with the HPA and in issuing a ticket of violation.

Conclusion 2-2: Physical examination methods are critical in detecting pain when performed by an examiner with sufficient knowledge of normal versus abnormal horse movement and posture and the ways that horses react to palpation if they are in pain. To better detect soreness, it is important that these

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 recommends 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 potential 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 performing 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)(2), which states that reexamination of the horse shall only be granted if the show veterinarian (not the competitor or any other persons) finds sufficient cause.

Methods Used to Detect Soreness

Observation of Horse Movement and Digital Palpation

Finding 2-3: As seen from 61 DQP inspection videos that the committee was allowed to view, inspectors do not carry out a sufficient observation of horse movement. During the visual inspection of the horse’s gait, the distance between the two cones is too short and not all horses complete an entire figure 8. The horse takes three or, rarely, four steps around the right cone and may pivot toward the cone on the left. Furthermore, the horse may not complete a sufficient straight-line walk.

Finding 2-4: VMOs are required to perform inspections according to APHIS protocols that are highly prescriptive. Recently APHIS adopted a process wherein a reinspection by a second VMO will automatically occur if the first VMO finds the horse bilaterally sore. This process requires both VMOs to make exactly the same findings before a violation ruling is made.

Finding 2-5: VMOs are required to use the pad of the thumb with only enough pressure to blanch the thumbnail and to follow a specific pattern of applying digital pressure when palpating the horse’s limbs during inspection. This prescribed palpation method for VMOs falls short of established protocols for lameness examinations.

Conclusion 2-3: During inspection, ideally a horse should walk around the cones in a figure-8 pattern. Expanding the figure-8 pattern to consist of two adjoining circles, each with a 10-foot radius, would allow for better observation of horse movement. The required straight-line evaluation could be done as the horse is walking to the top of the first circle and then back from the figure 8.

Conclusion 2-4: Prescriptive protocols, if not followed strictly by a VMO, may allow for a possible objection to a VMO’s finding by the horse custodian. Moreover, the required inspection by a second VMO may cast

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 following 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 requirement 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 examinations, 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 prescribed, 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.

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 Equestrian 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 competition horses and include all of the opioids, sedatives, local anesthetics, and nonsteroidal anti-inflammatory drugs (NSAIDs). These medications (along with their allowable concentrations) have been identified and are tested for by USEF, which has set the standards for medication testing for the entire nonracing equine competition industry in the United States, and other performance horse organizations. Blood testing for medications is not routinely done in TWHs.

Conclusion 2-8: Anti-inflammatory drugs (e.g., NSAIDs), the prevalent type of medication detected in samples from TWHs in 2014, are generally given to horses to treat illness or injury or to alleviate pain in some part of the horse’s body. Research indicates that NSAIDs, opioids, and local anesthetics may significantly reduce or abolish a sore horse’s response to palpation. Data collected through blood testing to determine the use of NSAIDs, opioids, local anesthetics, or sedatives in TWH competitions could be applied to correlate the use of these drugs in horses that are or are not identified as being sore.

Recommendation 2-8: Serious consideration should be given to testing blood of TWHs, using USEF’s rules and guidelines as a model, to detect medications administered to alter TWH response to palpation and for overall protection of TWH welfare and ensuring fair competitions. This would include random selection of horses, identified by microchip, at shows or sales. Championship shows should require testing of winning horses as well as randomly selected competing horses.

Variability of Pain Expression

Finding 3-1: Individual horses differ in perception and expression of pain. These differences are influenced by such factors as distractions and stressors in the immediate environment and the horse’s genetics, training history, temperament, and coping style.

Finding 3-2: Research has shown that horses’ responses to environmental stressors tend to overshadow their responses to pain. Hence, pain assessment scales used in veterinary research and practice recommend observing the horse in a quiet environment to ensure that the findings are valid and reliable.

Finding 3-3: Observation of 61 inspection videos revealed that some inspections were conducted in relatively quiet locations during a show whereas others were conducted in locations with loud noises and large numbers of people and other horses moving around nearby.

Finding 3-4: The “pain inhibits pain” effect (i.e., conditioned pain modulation) occurs when the pain of interest is inhibited by a pain induced in a different part of the horse’s body. During inspection, it is possible that pain in the lower limb and hoof that is being evaluated could be inhibited if the horse also experiences pain because of how it is being restrained by the custodian.

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 sensitivity 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 methods 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, physiological, 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 confirmed 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 veterinary care to assess pain and welfare state.

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 expressions 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 different inspectors. It is also important to determine the extent to which the facial expressions of pain correspond to current evidence of soreness during inspections, such as withdrawal responses to digital palpation and findings of noncompliance with the scar rule criteria.

Conclusion 3-5: One practical limitation to including facial expressions to assess pain during digital palpation 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 inconsistent 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 behavioral 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, researchers 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.

Finding 3-12: Most physiological measures do not discriminate between pain and other sources of autonomic 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 characteristics in this breed.

Recommendation 3-6: The decision to disqualify a horse due to soreness should be driven by an experienced 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.

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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):455–459.

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) in the form of acanthosis (thickening of the stratum spinosum layer of the epidermis) and variable degrees of hyperkeratosis (thickening of the stratum corneum layer of the epidermis). These skin changes are not incidental or insignificant and do not represent the normal character of the palmar aspect of the horse’s pastern. In addition, skin changes seen on the pasterns of TWHs are not observed on those of other breeds of horses, which also train with action devices but usually of lower weight compared to those used on TWHs.

Finding 4-2: The changes of hyperkeratosis and acanthosis, which were prominent in the biopsy specimens, do not normally occur without a previously inflicted injury on the pasterns. These changes are recognized as secondary, chronic lesions, and they do not provide clear evidence of the initial injury to the skin leading to these changes. They are, however, expected to correlate with the grossly detectable lesions of irregular epidermal thickening known as lichenification, a pathologic change most often caused by rubbing, scratching, or some other repeated trauma to the skin.

Conclusion 4-1: The primary injury to the pastern of horses from which skin samples were collected or of any of the TWHs presenting with lichenification of the skin of the palmar aspect of the pastern is not known. It is possible that action devices alone worn by walking horses could have led to the formation of these lesions; however, this seems highly unlikely if the federal regulation limiting the weight of the action device to 6 ounces was followed.

Conclusion 4-2: More studies are needed to determine if training practices that can cause soreness in TWHs also result in lichenification. A longer-term observation of horses that are subjected to training conditions identical to TWHs training for competition but without use of any chemicals or other agents known to have been used for soring is needed. These studies might elucidate at what point, if at all, during training epidermal hyperplasia and lichenification would develop and what particular training practices would cause these conditions. It is important that observations include periodic biopsy of the palmar aspect of the pastern to check for microscopic changes.

Conclusion 4-3: Studies are also needed to determine if epidermal thickening (hyperplasia) and lichenification are solely caused by the action devices worn by TWHs. This would require observing pasterns of walking horses that were not trained for competition but were made to wear action devices under circumstances identical to TWHs in training for competition.

Finding 4-3: The Horse Protection Regulations and scar rule were written without any microscopic evaluation of skin lesions from horses suspected of being sore. The scar rule language was based on a clinical evaluation of the skin only and has not been reviewed since its inclusion in the regulations.

Conclusion 4-4: The scar rule language is based on the assumption that certain lesions exist microscopically and that those lesions can be detected by gross clinical dermatologic examination and also that the terms used in the scar rule were used appropriately. In addition, it is assumed that the rule can be interpreted and applied in a consistent manner by VMOs and DQPs tasked with examination of horses for scar rule violations. None of these assumptions hold true today, and therefore the rule as written is not enforceable.

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: