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From page 74... ...
4 Review of the Scar Rule for Determining Compliance with the Horse Protection Act This chapter reviews the scar rule, its limitations, and what changes are currently documented re‐ garding the skin of Tennessee walking horses (TWHs) that are suspected of being sore. The chapter fo‐ cuses on the evaluation of changes in the skin of the forelimb of TWHs as part of the inspection process for ensuring compliance with the "scar rule" as defined in the Horse Protection Regulations. Evaluation of these changes is an essential component of the inspection process for detection of soreness in TWHs. Particular emphasis is placed on the accuracy and specificity of the language of the scar rule in light of changes that have occurred in the TWH industry since the scar rule was included in the Horse Protection Regulations. A suggestion for updating the language of the scar rule to accurately reflect the character of soring lesions is presented. Accurate recognition and documentation of the skin abnormalities found in TWHs determined to be in violation of the scar rule is essential for training inspectors to recognize these changes and for ensuring compliance with Horse Protection Regulations. An overview of the microscopic anatomy of the skin and a review of both the current clinical abnormalities and histological (microscopic changes)
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From page 75... ...
Review of the Scar Rule for Determining Compliance with the Horse Protection Act (a) The anterior and anterior‐lateral surfaces of the fore pasterns (extensor surface)
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From page 76... ...
A Review of Methods for Detecting Soreness in Horses The skin has three main layers, as illustrated in Figure 4‐2. Gross lesions of the skin are categorized as primary, indicating a change in a tissue that represents the effects of the original injury or disease as it first occurred. Primary lesions are the most useful lesions in determining the etiology or cause of an injury or disease. Examples of primary injuries of the skin include vesicles (blister) , papules, nodules, or lacera‐ tions. Secondary lesions of the skin, on the other hand, reflect changes in the tissue that occurred over a period of time after the initial injury (Figure 4‐3)
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From page 77... ...
Review of the Scar Rule for Determining Compliance with the Horse Protection Act FIGURE 4‐3 Examples of primary and secondary lesions of the skin. SOURCE: Hargis and Ginn (2011) . FIGURE 4‐4 Example of the evolution of a lesion over time. A primary lesion of a papule (palpable bump less than 1.0 cm)
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From page 78... ...
A Review of Methods for Detecting Soreness in Horses MICROSCOPIC EVALUATION OF SKIN BIOPSIES OF TENNESSEE WALKING HORSES FOUND TO BE IN VIOLATION OF THE SCAR RULE To date, no peer‐reviewed studies have been published on microscopic lesions of the skin from horses determined to have either skin lesions or other types of violations of the scar rule. In fact, the Horse Protection Regulations and the scar rule were written without any microscopic evaluation of skin lesions from horses suspected of being in violation of the HPA or scar rule. However, an unpublished but peer‐reviewed study (Stromberg, 2017) that evaluated 136 pastern biopsies (right and left pastern from each horse)
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From page 79... ...
Review of the Scar Rule for Determining Compliance with the Horse Protection Act FIGURE 4‐5a Photomicrograph of the caudal pastern of the skin of a horse included in the Stromberg study. The epidermis (long arrow) is markedly thickened. The stratum corneum (small arrow)
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From page 80... ...
A Review of Methods for Detecting Soreness in Horses FIGURE 4‐6 Lichenified skin on the mane of a horse. The skin is visibly and palpably thickened and there is a loss of hair. In this case, chronic rubbing to pruritus (itchiness) led to this change. SOURCE: Photo courtesy of P. E. Ginn, D.V.M. FIGURE 4‐7 Microscopic image of lichenification. The epidermis is markedly thickened by irregular hyperplasia of the stratum spinosum layer of the epidermis. The stratum corneum is also thickened and forms a layer of sloughed degenerated cells on the surface that exfoliates. SOURCE: Photo courtesy of P. E. Ginn, D.V.M. Lichenification is a pathologic change most often caused by rubbing, scratching, or some other re‐ peated irritation of the skin. The skin changes are not incidental or insignificant and do not represent the normal character of the palmar aspect of the pastern of the horse (Figure 4‐8)
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From page 81... ...
Review of the Scar Rule for Determining Compliance with the Horse Protection Act FIGURE 4‐8 Normal appearance of the skin of the palmar aspect of a horse. SOURCE: Photograph by J. Kevin Hahn, D.V.M. Used with permission. FIGURE 4‐9 Pastern of a chronically sored horse in violation of the scar rule. There is marked lichenification and alopecia (hair loss of the palmar surface of the pastern) . Note the exaggerated, thick, deep skin folds. This type of fold does not flatten with digital pressure. The gross lesions are consistent with the pathological changes (marked irregular epidermal hyperplasia)
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From page 82... ...
A Review of Methods for Detecting Soreness in Horses A horse included in the Stromberg study and documented as disqualified from competition at the 2015 Tennessee Walking Horse National Celebration was featured in an online article posted in 2016 that included a photograph of the horse's pastern at the time of disqualification (Billy Go Boy Chat, 2016) . The photograph of this horse shows gross lesions of erythema (redness)
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From page 83... ...
Review of the Scar Rule for Determining Compliance with the Horse Protection Act EVALUATION OF THE SCAR RULE CRITERIA FOR COMPLIANCE WITH THE HORSE PROTECTION ACT The HPA and scar rule were written without any microscopic evaluation of skin lesions from horses suspected of being sore. The language of the rule was based on clinical evaluation of the skin only and has not been reviewed since its original inclusion in the Horse Protection Regulations and its implementation in 1979. Veterinary dermatopathology is now a well‐recognized field of study and provides a solid frame‐ work for the accurate evaluation and characterization of skin lesions in animals. The committee believes that the rule should be revised using well‐defined current medical terms that accurately describe the le‐ sions seen today from both the clinical and histopathological standpoints. Basis of the Scar Rule The language of the scar rule is based on the assumptions that certain lesions exist microscopically, that those lesions can be detected by gross clinical dermatologic exam, and 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 Animal and Plant Health Inspection Service (APHIS) veterinary medical officers (VMOs)
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From page 84... ...
A Review of Methods for Detecting Soreness in Horses enforceability. The scar rule also refers to bilaterally uniformly thickened epithelial tissue, which is con‐ fusing. The thickening of the epidermis present in the biopsy specimens reviewed is not "uniform." It is irregular and characteristic of lichenification. The lesions of cardinal signs of inflammation such as edema and erythema (reddening) of tissue and also pain and the presence of moisture can likely be detected by most examiners. The name of the rule itself, "the scar rule," is very misleading but has been in common use for dec‐ ades and refers to recognizable lesions in violation of the rule. It is still important to correct the language of the rule if it is to be enforceable in a court of law. Scars have not been documented microscopically in TWHs that have been found to be sore. A scar is an area of tissue where the normal components and organization of the tissue have been lost and replaced by fibrous connective tissue. Scars can be grossly evident, but there is no reliable documentation in the literature of a gross lesion found on a sore TWH that is compatible with a scar. Scars were very likely present in the lesions seen on sore TWHs before the enactment of the HPA. Lesions present today are more subtle, and the limited microscopic studies that have been done have not documented scars in horses determined to be in violation of the scar rule, which renders the usage of the term "scar" inappropriate. History of Skin Lesions in Tennessee Walking Horses Suspected of Being Sore Prior to the enactment of the HPA and the implementation of the scar rule, lesions in sore horses were grossly evident and located primarily on the anterior skin of the dorsal and palmar (caudal)
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From page 85... ...
Review of the Scar Rule for Determining Compliance with the Horse Protection Act 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. Finding 4‐3: The Horse Protection Regulations and scar rule were written without any microscopic evalu‐ ation 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 microscopi‐ cally 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 inter‐ preted 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 en‐ forceable. 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. BOX 4‐1 Ultrasonography to Study Pastern Tissue Injury in Tennessee Walking Horses Ultrasonography or the use of ultrasound equipment to evaluate healthy skin and pathological lesions is a method that is gaining popularity (Mlosek and Mainowska, 2013) . In veterinary medicine, ultrasonography is now routinely used in various applications to help in diagnosis and therapy. With the availability of portable laptop‐size units, ultrasonography can now be conveniently performed in a barn (Baird, 2017)
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From page 86... ...
A Review of Methods for Detecting Soreness in Horses RECOMMENDATION 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. REFERENCES Baird, S. 2017. Ultrasound imaging and horse health. https://www.mvsequine.com/ultrasound‐imaging‐and‐horse‐ health (accessed November 20, 2020)
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