"COMPLETE RIDER" YOUR #1 HORSE DESTINATION

Republished with permission from UC Davis Pastern Dermatitis in Shires and Clydesdales by Dr. Gregory L. Ferraro Every individual who has been charged with the care and maintenance of draft horses is familiar with the chronic dermatitis that plagues the pastern areas of their charges. Traditionally known as scratches, grease heel or cracked heels, this condition is the bane of existence for horsemen who need to keep their horses in fit and working condition. It is a localized skin condition that never seems to go away despite constant care and the application of a wide array of medicants, potions and topical therapies. While this condition is widely evident throughout the horse industry, it is within the Shire and Clydesdale breeds that it manifests itself in its most severe and debilitating form. The disease processes start at an early age, progress throughout the life of the horse and often ends in disfigurement and disability. It first appears as small, well-demarcated, multiple ulcerations of the skin at the rear of the pastern in any one or all of the four legs. These ulcerations are covered with crusty exudative material and often bleed, especially during exercise and work. These small sores may seem to respond initially to treatment with topical medications but often reverse course, only to progress in severity and multiply in number. These multiple lesions often will coalesce into larger and more intractable areas of skin ulceration. They then become chronically infected, produce copious amounts of foul-smelling exudate and chronic thickening of the affected areas of skin. Over time, these lesions spread up the leg, often affecting the skin as high as the knee and/or hock joints. These lesions are, at the very least, irritating and bothersome to the horses and, at times, can be quite painful. Severely affected individuals often exhibit generalized swelling in all four legs. In older, chronically affected horses, this enlargement of the lower limbs becomes permanent and is accompanied by thickened skin folds and the formation of large, well defined, hard nodules (called "grapes" by previous generations of horsemen). These nodules can become quite large, often "golf ball" or even "baseball" in size. The nodules themselves then become a mechanical problem because they interfere with free movement and are often injured or damaged during work. The shaved leg of a draft horse with pastern dermatitis showing chronic irritation and thickened skin up the leg. Horsemen and veterinarians have been arguing over the cause and possible treatments for this condition for decades. Everything from mange mites to bacteria, fungi and chemical or plant irritants has been implicated as possible causes. Even the horse's own hair, the luxuriant "feathers" that descend over the lower leg and pastern, have been blamed because it holds moisture and thereby provides the warm and wet environment on the skin surface which enhances the growth of fungi and bacteria. In recent years, some veterinarians have felt that the condition was somehow related to a photosensitivity problem because the lesions were most evident on white legs. (In fact, they are also prevalent on dark limbs, just harder to see, especially in those horses with well-grown feathers.) In the late 1980s, a Dr. Tony Stannard of the UC Davis School of Veterinary Medicine made some preliminary microscopic analyses of the diseased areas of skin and classified what he saw as "Pastern Leukocytoclastic Vasculitis." This rather long and complicated sounding moniker was meant to denote that the condition was caused by degenerative changes in the small microscopic blood vessels of the affected skin. His work provided the first indication that the common grease heal of draft horses might, in fact, be a definable disease entity. Unfortunately, his research in this area was cut short by his untimely death. Recently, because of the interest, cooperation and financial support from Ayrshire Farms of Upperville, Virginia, scientists at the UC Davis Center for Equine Health have again taken up this work. The research team, led by Dr. Verena Affolter, has catalogued and followed the progression of the lesions, biopsied them, analyzed the harvested tissues microscopically and subjected them to various equine antigens. These investigators have confirmed what Dr. Stannard suspected; that the degeneration of the vasculature has an immune-mediated component which is central to the production of disease. While the work is neither complete nor conclusive as to the cause and effect of the disease, the research so far indicates that much of the damage caused to the skin and subcutaneous tissues of the lower leg and pastern may be a result of the horse's own immune response to an inciting irritant. In other words, the initial agent which attacks the skin is not important. A type of bacteria, fungus, or mange mites afflicts the horse's skin which initiates a hyperactive or misdirected response by the horse's own defense mechanisms. The animal's own immune system then becomes the actual perpetuating cause of the problem. This "hyper" reaction by the body persists long after the original irritant (mite, bacteria, etc.) is gone which partially explains why the list of failed treatments is so long. Whatever particular treatment one employs, it may eliminate the particular pathogen present, but once that one is eliminated, another which is not susceptible to the medication chosen takes over because the horse's skin is too busy fighting with itself to defend against any new invaders. So the pastern dermatitis which has forever plagued the draft horse enthusiast is not, in fact, a simple infection by some single identifiable and easily eliminated microbial agent, but rather the manifestation of an extremely complex immune-mediated disease phenomenon. These types of medical mysteries are difficult to unravel; indeed, the UC Davis researchers expect the ultimate solution will take years to define. While the work is ongoing and far from complete, the factual information developed so far does lend itself to some practical recommendations regarding the care of horses affected by this condition. Cleanliness is extremely important to the long-term control and management of these lesions. The hair over the affected areas must be washed and dried carefully on a daily basis. This removes the dirt, debris and exudate that promotes and harbors the complicating microbes. While the clipping or removal of the feathers may facilitate the initial treatment of severely affected animals, it is not, in and of itself, a treatment for the condition; nor is hair clipping absolutely necessary for successful control of the problem. Topical antimicrobial or antifungal preparations are only marginally helpful because; (1) while they may kill the particular pathogen present in the lesions at the moment, this organism will be, most certainly, replaced by one which is not susceptible to the product being used and, (2) no topical product can affect the underlying immune mediated disease. Likewise, it makes no sense to use highly toxic or irritating topical agents such as lead acetate paste or coal-tar type preparations because, while they may kill everything in sight (including the groom), they do nothing to counteract the basic disease and may, in fact, promote further debilitation of the skin. One topical treatment that has shown, over time, to be useful in the control and management of the skin lesions is the daily application of sulfur based preparations. These come in two forms. The first is as a wetable sulfur dusting powder commonly used for disease control in plants. This powder is readily attainable at nurseries and other garden product stores. The powder can be mixed with mineral oil to form a thick "milk shake" like solution which can then be massaged deeply into the affected areas of the skin after the legs and hair have been carefully washed and dried. The key here is that the preparation must be carefully worked down into the affected areas of the skin. Simply pouring it on the hair or squeezing some on the lesions will not be successful. The obvious downside to this treatment is that it is very time consuming. The second method of utilizing sulfur as a treatment is through the use of sulferated lime solutions. These are commonly recommended for dermatitis in cats and dogs (LymDyp, DVM Pharmaceuticals, Inc.) and are available through most veterinary supply outlets. This treatment is also only effective when one is careful to soak the affected limbs long enough in the solution to ensure that the sulfur comes into intimate contact with the skin for a sufficient period of time. Additionally, mange mites definitely must be controlled as they can be both an inciting cause and a compounding stimulant to the condition. To control infestation on individual horses, a 0.25% fipronil solution (Frontline), the commonly used canine flea and tick control agent, can be used. This solution can easily be periodically sprayed on the horse's legs to prevent infestation. The hair of the entire leg must be sufficiently dampened from at least the coronary band to well above the knee and hock on all four legs to assure protection. In conjunction with the treatment of the individual horse, the stalls, wash racks, feed rooms and other working areas of the barn should also be cleaned and sprayed periodically with a permethrin aerosol spray to remove environmental mite infestation. Systemic corticosteriods are only effective when used in relatively high dosages. Therefore, they can only be used on a short-term basis in severely affected animals to assist in establishing a more stable basis for longer term therapy. Topical steroid preparations are, by and large, ineffective. Systemic antibiotics are useful only if the condition is temporarily complicated by a secondary bacterial infection. Topical antibiotics and anti-fungals, as mentioned above, are only marginally useful and must be changed at least every third day to have any effect at all on controlling microbial populations. In summary, let it be re-emphasized, that the skin lesions we see on the pasterns of Shires, Clydesdales and perhaps other breeds of working horses are not isolated infections or skin abrasions, but the result of a very complicated and, as yet, ill-defined immune-mediated systemic disease. While veterinary medical scientists are working hard to better understand this disease, a cure is a long way off. Control is possible through the implementation of a diligent, daily program of cleanliness and decontamination. It must be fully understood that one who contemplates imbibing in the pleasure and enjoyment derived through the use and ownership of heavy horses, must also be willing to assume the sometimes burdensome responsibility for the proper care and maintenance of these "most noble" of steeds. For more information or to donate any horses to this project, please contact Dr. Gregory Ferraro at (530) 752-6433 or via e-mail at glferraro@ucdavis.edu. The Horse Report is Copyrighted © 2001 by the Regents of the University of California. Use of this material for re-publication is allowed only by permission of the Center for Equine Health. The Center for Equine Health does not provide veterinary medical services or specific advice via e-mail or the Internet. Due to time constraints, we may not be able to respond to every e-mail message, but we appreciate your input. Always consult your veterinarian in matters regarding the health of your animals The research conducted by the Center for Equine Health is supported with funds provided by the Oak Tree Racing Association, the State of California pari-mutuel fund, and contributions by private donors. --------------------------------------------------------------------------------   Immunization Schedule for Horses|West NileVirus|ColicBasics|Lameness?|Tapeworms | Mare Reproduction Loss|Foal Vaccination for Equine Influenza

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