"COMPLETE RIDER" YOUR #1 HORSE DESTINATION
Equine Skin: the Vital Protective Layer
Republished with permission from UC Davis
CEH's own stallion San Par exhibits the bright shiny coat that goes with healthy skin.
The shining glistening coat of a horse in good health is the image artists love to capture on paper and canvas. The way the light reflects a myriad of colors from the slick, silky hair...it can be literally stunning, and one can't help but want to touch that sleek coat. But when there's a problem with the skin, it can be heartbreaking to watch the once shining coat turn dull and frizzy with dry flakes and/or bald patches. The horse may be so uncomfortable that it rubs up against anything it can find to relieve the inscrutable itch, to the point of causing great scabs open to infection.When we think of equine health, we usually think of orthopedics, performance, infectious disease, etc.; however, it's the skin that often shows the first signs of ill health. When the horse's health or nutrition is compromised, the skin's blood supply, which carries vital nutrients, may also be affected. In fact, the hair and skin can be like a record, showing the signs of previous disease, stress and changes in nutrition for months.
The skin acts as a protective covering for the entire body. It is comprised of many layers organized into three main sections: the epidermis, the dermis and the subcutis. The epidermis is the outer section without blood vessels of which the hair, hooves, chestnuts and ergots are extensions. The dermis is the middle and thickest major section of the skin that provides most of the skin's bulk. It is comprised of connective tissue fibers made up of collagen and elastin. The dermis has a rich supply of blood and cells that mediate the inflammatory response. The subcutis is the innermost section of the skin and it is composed of fat cells and thin strands of collagen containing connective tissue. The nerves and blood vessels supplying the skin weave their way through the strands of connective tissue to reach the overlying dermis.
Skin problems occur due to a variety of causes. Bacterial, viral and fungal infections as well as parasites can cause skin reactions that sometimes render a horse temporarily unusable. Just like people, allergies also affect horse's skin, resulting in various sized lumps and bumps, with or without itching or hair loss, which may be very sensitive to touch. Problems with the horse's immune system can cause serious skin problems and there are some genetic skin conditions that can also render a horse unusable. Photosensitization results from concurrent exposure to ultraviolet radiation (sunlight) with certain foods or medications. This can cause ulcerations and secondary infections, usually of the white or lightly pigmented areas.
Over the last decade, much of the advances in equine dermatology at UC Davis were directly or indirectly attributable to the late Dr. Tony Stannard, as well as Dr. Peter Ihrke. These advances include recognizing the importance of equine auto-immune skin diseases such as pemphigus foliaceus commonly seen in Appaloosas, bacterial skin diseases, and definitions of several genetic skin diseases. After Dr. Stannard's untimely passing in July of 1997, colleagues from around the country collaborated in publishing his observations in the form of "Stannard's Illustrated Equine Notes" as a special edition of the international refereed journal Veterinary Dermatology. This publication will doubtless serve as a reference in all fields of equine dermatology for many years to come.
Currently, UC Davis researchers headed by Dr. Stephen White are studying several areas of equine dermatology. Hyperelastosis cutis is a genetic disease that primarily affects Quarter Horses. The disease results in a lack of cohesion of the superficial layers of the skin, especially in the saddle area, which renders many of these horses unsuitable for riding. Assisted by a grant from the CEH, UC Davis veterinary dermatologists, in conjunction with pathologist Dr. Verena Affolter, geneticist Dr. Danika Metallinos, and co-researchers at Colorado State University, are investigating the underlying genetic defect, as well as the inheritance pattern of this disease.
UC Davis researchers are also investigating auto-immune skin diseases in the horse. These diseases occur when the horse's own body "attacks" itself. The immune system goes haywire and treats certain parts of the skin as foreign invaders, sending out antibodies and other immune system components. The result is often inflammation, crusts, and/ or open sores. UC Davis researchers, led by Dr. Verena Affolter, are studying this problem in Clydesdales and Shires, breeds that appear to have a predisposition for developing chronic pastern dermatitis. Sometimes, certain breeds have a tendency to develop a particular disease. UC Davis researchers are investigating these diseases and the genetics behind these tendencies.
UC Davis researchers are also studying treatment modalities for various auto-immune skin diseases. In dogs and people, doctors commonly use a drug called azathioprine to treat these diseases, however, there have only been a few cases of its use reported in horses. The first step in this investigation to identify an important azathioprine-metabolizing enzyme in horses called thiopurine methyltransferase (TPMT). Future research will focus on the actual pharmacodynamics (how the substance acts in the body) of azathioprine in the horse, in conjunction with equine pharmacologist Dr. Cynthia Kollias-Baker.
Another area of skin problems that UC Davis researchers led by immunologist Dr. Laurel Gershwin are investigating involves the immune system and improving allergy testing. These researchers are discovering how the immune system works which provides information on allergic reactions. This research is designed to develop improved allergy testing techniques for horses.
Dr. Alain Theon, an oncologist, is also conducting extensive tumor research on horses at UC Davis. He has evaluated various treatments for sarcoids and melanomas, two common skin tumors that can render a horse unusable. Currently, he is investigating the possibility of designing a specific vaccine that can stimulate the horse's own immune response to target skin tumors and cause their regression.
As researchers continue to make advances in equine medicine, dermatologists will have more tools at their disposal to use for the diagnosis, prevention and treatment of skin problems in horses. Veterinarians, just like horse owners, want to restore those shining glistening coats and UC Davis dermatology research will contribute vital information toward that goal.
HELPFUL TIPS
Skin Problems
In general, most skin problems in horses can be divided into several basic areas:
pruritic (itchy) skin diseases
hair loss without itching
nodules (lumps)
loss of pigment
sun-induced damage (photosensitization)
excess scaling
Any of these clinical signs can cause loss of function and/or unacceptable appearance; when they do, it is time to call the veterinarian.Avoid the use of steroids/steroidal ointment until you know the problem is not infectious. The use of steroids can cause infectious conditions to rapidly spread.
The Horse Report is Copyrighted © 2001 by the Regents of the University of California.
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.
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