Equine Skin Problems and Causes
- Aug 1, 2000
Skin is a horse's largest organ, and it's the only organ that an owner can examine in its entirity and monitor on a daily basis. The skin not only acts as a barrier to outside insults, but protects a horse's internal structures, allows the majority of body heat dissipation, and serves as a monitor for general wellness or illnesses. The skin also is subject to attack on a number of fronts, ranging from infectious bacteria or fungus and biting insects on the outside, to liver, nutritional, and other problems on the inside. The results can range from mild (dandruff) to serious (skin cancer).
While there are varied approaches--and many products--available to the horse owner to treat skin afflictions, the best approach is prevention. If, however, your horse does develop a skin problem, it should be addressed immediately. Determining the exact cause of the skin condition and treating it appropriately will ease your horse's suffering and perhaps result in catching a serious health problem early enough to cure it without loss of competition or riding time. To do this, you should involve your veterinarian. Partner with him/her to ensure that the chosen treatment is effective against the problem your horse is facing. This will keep you from wasting treatment time, and perhaps allowing a minor skin condition to become a major one.
Only Skin Deep
A horse's skin is its largest body organ, ranging from 12%-24% of the animal's weight, depending on age. The skin consists of various cellular and tissue components, which are broken down into two major layers: the superficial covering of stratified squamous epithelium called the epidermis, and a deeper layer of dense, irregular connective tissue called the dermis or corium. Scientifically, there are many other "layers" to skin. The dermis in most areas of the horse's body consists of a superficial, tougher layer called the stratum corneum and a deeper layer that grows called the stratum basle or stratum germinativum. It is in the deepest layers of this portion of the skin that cells divide and begin to push their way into the more superficial layers. These deep layers also are close to the blood vessels, which supply nutrients to the growing cells.
As the cells are pushed closer to the skin surface (and farther away from the nutrients), they begin to die and flatten out. This process is known as keratinization and cornification. Then, these cells degenerate and flake off the surface of the skin in what we normally call dandruff.
The proper functioning of this superficial layer is dependent on the structural arrangement of the keratin it contains and perhaps on its lipids (fats and fat-like substances characterized by being water-insoluble). Lipids have an effect on the waterproofing capability of the skin and the absorption of agents into the body.
The arteries, veins, capillaries, and lym-phatics are concentrated in the dermis (deeper layer). While nerve fibers are found abundantly in the dermis, they also extend into the epidermis. Hair follicles have many sensory nerves. In some animals, hair follicles are complex. In horses, however, they are quite simple, with a single hair emerging from each pore.
The hair goes through periods of growth and inactivity. Shedding, for example, is a seasonal event and represents the loss of inactive hair as a new growth takes its place.
The major function of a horse's skin is protection. The hair, first of all, provides mechanical protection. It also serves as an important filtering system and insulator. The superficial layer of the epidermis is a highly developed, tough, durable, flexible membrane that serves as a chemical and waterproofing structure. If it were removed, the skin would act like a mucous membrane that could be easily permeated by a variety of agents. Its ability to function properly can be compromised by disease or injury.
The skin also offers protection against the sun's rays. Ultraviolet light is filtered by the coat and absorbed by melanin granules in the epidermis and hair.
The horse's skin is highly important in thermal regulation. Research has shown that more than 70% of dissipation of body heat is through sweating. (Respiratory heat loss makes up most of the remainder.)
When an owner and veterinarian are working with a horse which is suffering from a skin problem--or the team is trying to prevent such problems from happening--nutrition plays a key role. Skin is influenced from the outside and the inside.
The Pain And Itch
Basically, skin diseases that afflict horses can be divided into two groups--those which arise from infection (either by germs or parasites), and those due to causes other than infections. Complicating the issue is the fact that, just like humans, horses can suffer from allergies or internal problems that affect the skin.
The inclusive term for inflammation of the skin is dermatitis. It can be produced by many agents, such as external irritants, burns, allergens, trauma, or infections of bacterial, viral, parasitic, or fungal origin. It also can be associated with systemic diseases.
The most common sign of dermatitis is scratching as the horse rubs the affected body part against fences, walls, posts, handlers, other horses, or anything else that is in reach. Then comes swelling and redness, followed by raised or bumpy spots on the skin. As the problem progresses, there could be oozing, crusting, and scaling.
When a dermatitis problem surfaces, the most important thing is to determine the cause. Many skin problems can look the same, but be vastly different. Treatment would be completely different, for example, if the horse were suffering from a fungal infection than it would if the problem were the result of an allergy. Also, if the owner thinks that a horse has ringworm and treats it (ineffectively) for ringworm, and in fact the horse has an internal condition causing a manifestation on the skin, problems multiply. The original cause of the skin affliction goes untreated and potentially gets worse, and the on-going treatment the owner is using might result in--guess what--a skin irritation.
A skin biopsy is necessary in some cases to determine the exact cause of a dermitis. This requires not only a veterinarian to take a sample, but that the owner assist in getting a sample from the most recent "outbreak" area. Knowing your horse, and knowing which lesions are the newest, will help your veterinarian take an appropriate sample.
Another reason owners should partner with their veterinarians in determining the cause of a skin problem is to prevent spread of those which are contagious. This will protect other animals, and potentially lead to management changes to avoid similar problems in the future. If the problem was nutritional or caused by an external source, other horses can be assessed to determine if they could be susceptible to the same affliction.
An owner should think about the cumulative effect of managing each horse. Simply put, owners should limit what they put on the horse's skin. Over-use of sprays, potions, or lotions--or use of multiple products at the same time--can cause more problems than they solve. Elbow grease is a great product for the horse, as proper grooming stimulates the skin and underlying tissues, gets rid of dead skin on the surface, and offers the owner a chance for personal scrutiny and a hands-on tour of the entire surface of the horse's body.
There are many problems--common and uncommon--that can manifest themselves in unhealthy skin. Following is some general information on some of those problems. One thing to remember is that all skin diseases that itch are worse when you add in sun, heat, or dirt; again pointing to the fact that good management is important.
Pyoderma is the scientific name for acne. It is an infection characterized by the formation of pus. Acne is actually an inflammation of the hair follicles. The cause of the disease is pyogenic (pus forming) organisms that have gained access to the hair follicles. It will be seen most frequently in parts of the body exposed to friction from saddle or harness. It also can be transmitted via biting flies.
An afflicted animal will show signs of tenderness when the affected body part is touched. When mature, a yellow point appears at the affected spot. Shortly thereafter, it will rupture, eliminating pus. Normally, in the wake of recovery, a permanent mark is left, frequently in the form of white hairs.
When pyoderma develops, irritation of the affected area through continued saddling or harnessing should be avoided. Bathing the area in warm antiseptic solutions such as hexachlorophene or povidone-iodine can be helpful. The problem can be either superficial or deep. In either case, the recommended form of treatment is administration of antibiotics.
Horses with this affliction, put simply, can't sweat. And when a horse can't sweat, it loses its thermoregulatory capability. It is a condition that can completely compromise a horse's ability to perform. Anhidrosis is pretty much climate-specific. It is found in areas with a hot, humid climate, such as Florida during the summer months.
No one is quite sure what causes anhidrosis, and there is no effective way to treat it other than moving affected horses to a cooler climate. Quite often, racehorses which suffer from anhidrosis in Florida will show no sign of the affliction when moved to the Midwest during the height of the southern hot weather cycle.
Pityriasis is the scientific term for dandruff, a condition in which the skin becomes scaly and the coat dry and dirty. In some instances, the hair will fall out. A lack of grooming and poor nutrition often are the culprits. Good grooming and a balanced diet usually can eliminate the problem, although some horses will need specific nutritional supplementation.
Mane and tail eczema is a condition that many horsemen have encountered. It is a dermatitis that sometimes is attributed to dirt and neglect, but it also can be from tick bites or pinworms. It frequently shows up on the tailhead and is called to our attention when the horse backs up to a post and begins rubbing. Later, the skin becomes thickened, hard, and scaly. Washing the tail head or mane area with disinfectant soap or deworming for pinworms can help eradicate the problem.
Hives is a common condition in the summer months in horses. Generally, the cause can be traced to allergic reactions to plants or bedding material.
The conventional treatment approach involves administration of steroids.
In the same general category as mange is pediculosis--the scientific term for infestation by lice. Horses can harbor two species of lice. They are the horse biting louse (Damalinia equi), and the horse sucking louse (Haematopinus asini).
Afflicted horses will show signs of itching by constantly rubbing and biting at affected areas. Lice are most often found in unthrifty horses kept in unsanitary conditions. In a severe infestation, the horse can lose patches of hair.
Infestations are more apt to occur during the winter, when hair coats are long. Lice can be quickly eradicated with spray-on or rub-on insecticides, a variety of which are available commercially.
Mange is a contagious skin disease caused by one of several species of mites. The disease is transmitted when larvae, nymphs, or fertilized females are transferred to a susceptible host. Mange can be transmitted directly from horse to horse, indirectly through contaminated objects that harbor the mites, or through contaminated stabling quarters.
Mange is characterized by loss of hair, itching, and intense irritation to the skin. In severe cases, this can lead to debilitation. In drastic instances, it can lead to death.
Conventional treatment of afflicted horses consists of applying mite-killing solutions by spraying, rubbing, or dipping. These solutions are available commercially.
This is a condition in which lightly pigmented skin is hyperactive to sunlight due to a photodynamic agent in the skin. Horses with pink noses are good candidates for this affliction. Those affected will demonstrate discomfort and will seek to scratch or rub the affected area. A reddening of the skin will develop rapidly and can be followed by swelling and, later, scab formation.
Afflicted horses should be kept under cover, such as in a barn, during the day, and allowed to graze in the evening hours. The months of June, July, and August pose the greatest danger to photosensitive horses.
This condition also can be a manifestation of an internal condition, so consultation with a veterinarian is advised.
Another form of dermatitis that can affect horses is dermatophilosis, more commonly known as rain rot or rain scald. This troublesome bacterial infection is most common in wet, humid climates. It will crop up frequently in southern states, for example, but is rarely seen in the Great Plains or Rocky Mountains.
The natural habitat of Dermatophilus congolensis, the ususual bacteria that causes the skin problem, is unknown, but many researchers believe that it lives in the soil. However, attempts to isolate it from soil have been unsuccessful. It has been isolated only from the skin of various animals, and it is restricted to the living layers of the epidermis. Infected animals are considered the primary reservoir.
The bacteria that cause rain rot can live in dormancy within the skin for some time and become active when the skin is compromised in some way, such as prolonged wetting by rain, high humidity, high temperature, or attacks by biting insects. When the infective zoospores reach a skin site where the normal protective barriers of the skin are reduced or deficient, they set up shop and infection is the result.
Zoospores germinate to produce hyphae (threadlike tentacles), which penetrate into the living epidermis and subsequently spread in all directions from the initial attack site (usually a break in the skin). The result is an acute inflammatory reaction.
The good news in the case of an acute infection is that the invasion by the hyphae ceases in two to three weeks and the lesions heal spontaneously. In chronic infections, however, the affected hair follicles and scabs are sites from which intermittent invasions of non-infected hair follicles and epidermis occur. Moisture facilitates release of zoospores from pre-existing lesions, and their subsequent penetration of the epidermis to establish new sites of infection. Hot weather and high humidity also can be indirect factors in that a wide variety of biting insects hatch and become active under those conditions, compromising the skin's protective function.
Horse owners with animals which spend most of their time outdoors in the wet, rainy season would do well to examine the animals periodically for rain rot. A visual evaluation won't get the job done, especially during the wet winter months when the horses have full coats of hair. A hands-on examination is the most effective. The infected horse usually will have a series of bumps along the back and croup. When rubbed, the "bumps" might come free in the form of scabs with a small, hairless spot of skin showing. Unlike ringworm, rain rot is not itchy.
While the infection is relatively easy to diagnose in the above manner, a definitive diagnosis can be made only by your veterinarian taking a culture and testing it in a laboratory.
The conventional treatment of infected animals often involves intra-muscular injections of procaine penicillin and streptomycin.
External treatment with disinfectants that contain a cresol or copper salt base can decrease the spread of infection if applied at times when transmission is likely, according to medical literature. Controlling biting insects by applying insecticides also can be effective in preventing the skin breaks that allow the causative agent to get a foothold.
Nature's best cure for rain rot is warm sun and dry weather.
One form of dermatitis that can and does afflict horses is "ringworm," known scientifically as dermatophytosis. While the skin blemish can look like a ring or circle, there are no worms or parasites involved. Instead, ringworm is caused by a fungus. There are many sorts of this fungus, and the horse is susceptible to a number of them. Ringworm infection can be spread directly from horse to horse and by using common grooming tools, saddle pads, harnesses, and saddles. Humans can spread ringworm to horses, and vice versa.
Ringworm is an infection of keratinized tissue by one of several types of fungi, collectively known as dermatophytes, thus the scientific name of dermatophytosis. Under most circumstances, dermatophytes grow only in dead, keratinized tissue. Horses most susceptible are the young, debilitated, or animals whose immune systems have been compromised.
Infection begins in a growing hair, eventually causing it to break off just above the surface, or in the outer surface of the epidermis. Fungal culture is the most effective and specific means of diagnosis.
The two types of ringworm encountered most commonly in horses are caused by Trichophyton equinum, the primary cause, and Microsporum equinum, which is more prominent in locales outside the United States. T. equinum is responsible for a type of ringworm that was introduced during the World War II and brought to these shores by imported horses.
This type of ringworm produces skin lesions that appear as small, rounded spots, a quarter of an inch to an inch in diameter. The lesions eventually form blisters and break, leaving scabs. This form of ringworm is easily transmitted to humans and is a notoriously itchy form of the disease.
A variety of Trichophyton that also attacks horses is T. mentagraphytes. It can be carried not only by humans and horses, but also by rats and mice. They can infect foodstuffs or wind up in horse mangers or feeding areas. With this type of ringworm, lesions first make their appearance on the forehead, face, neck, and at the root of the tail, but they also can spread to other parts of the body. The oldest part of each lesion is at its center, and its growth spreads from the edges. The lesions are grayish in color and form crusts on their surface from which broken hairs protrude.
While ringworm usually is a self-limiting disease, topical care of the affected area (as advised by your veterinarian) usually will improve the way the horse feels and the appearance of his coat. However, it is difficult to attack the condition itself with topical medications because the causative agents are residing at a deeper layer than most topical medications can reach. When ringworm strikes, you should immediately disinfect all grooming equipment. If possible, the horse should be isolated to prevent further spread of the disease.
Suggested in medical literature as part of the conventional approach are washes or sprays of 0.5% lime-sulfur; 0.5% sodium hypochlorite (1:10 chlorine bleach); 0.5% chlorhexadine solution; or 1% povidone-iodine. It is recommended that the desired medication be applied to the entire body of the affected animal on a daily basis for five to seven days, then weekly until the infection is controlled.
If a horse should contract ringworm, it is suggested by veterinarians that the thick crusts be removed gently with a brush and mild soapy water and the contaminated material burned.
Ringworm is most common during the fall and winter, but can crop up at any time. Exposure to sunlight can assist in healing of the lesions, but again, sweating can cause the horse to itch worse, rub the affected area more, and could lead to skin infection.
Saddle Sores Or Galls
A condition that is somewhat similar to acne involves saddle sores. The areas of skin under the saddle on riding horses and on the shoulder area of driving horses are frequently the sites of skin and soft tissue injury. Clinical signs will vary, depending on the depth of injury as well as complications from secondary infections.
Frequently, the condition starts as an acute inflammation of the hair follicles and progresses to a pus-producing condition. Affected areas will have hair loss and possibly be hot, swollen, and painful. Advanced lesions are termed "galls." In severe cases, abscesses can develop.
The cause of saddle sores usually is ill-fitting tack or, occasionally, dirty saddle pads. When the condition arises, the first line of treatment is absolute rest of the affected parts and a readjustment of the tack that caused the problem in the first place. During the early stages, astringent packs (Burow's solution or 2% lead acetate) can be helpful. Chronic lesions and those superficially affected can be treated by warm applications and massaged with stimulating ointments or with antibiotics.
Horses can develop a benign form of skin cancer called sarcoids. The conventional treatment approach normally is to inject drugs into the growth and use cryotherapy or freezing of the tissue. (For more on sarcoids and melanomas see The Horse of June 1999.)
There are a number of names and terms for the condition many horsemen call scratches, such as grease heel, mud fever, cracked heels, white pastern disease, and dew poisoning. The affliction usually begins with a softening of the skin behind the fetlock and the heel. It often afflicts a horse which is residing in a wet, muddy, or marshy area. As the condition progresses, the affected body part is invaded by tiny mites. They feed on the epidermal debris, and in the process, cause irritation to the afflicted area. The next stage can be a form of staph infection followed by a fungal invasion. This results in inflammation that is accompanied by crusty, scabby bumps or lesions.
The first step in the treatment, whether holistic or conventional, is to remove the horse from the wet environment. If the affliction is in the early stages, washing the area with warm water and soap can be effective. Application of a wetness barrier, such as Desitin ointment, can help protect the area.
Skin problems can be caused by viral invasions. A case in point is papillomatosis, or warts. An incidence of warts would be more common in younger animals than in adults.
In horses, small, scattered warts can occur on the nose and lips, presumably at the site of abrasions when foals nuzzle each other. Warts in young horses are not uncommon, but normally they will disappear, and the animal will have developed an immunity against future attacks by the virus.
Warm, sunny weather and being turned out on grass also facilitates the disappearance of warts.
If warts become a herd problem, the conventional med-ical approach might include vaccination. However, because warts are so species specific, what works for one species might not work for another. The most effective vaccination approach has been with a suspension of ground wart tissue in which the virus has been killed with formaldehyde.
Others: Midline Dermatitis, Sweet Itch, and Similar Conditions
Many horses get intensely itchy skin in various parts of their bodies. Basically, their immune systems are over reacting or they are having an allergic reaction to insect bites, plants, or bedding material.
This can be a debilitating condition during the summer months if they rub their skin raw and are very uncomfortable.
Sweet itch is a term applied to horses in some geographical areas which are attacked by a particular type of gnat. These horses generally rub their manes and tails, and sometimes rub out all of the hair.
The wise horse owner will know that the horse's entire body is involved when the skin is affected, and will make certain that a horse is in good physical condition from exercise and a proper diet. Com-mon sense management and advice from your veterinarian can stop skin problems before they interfere with your horse's health.
About the Author
Les Sellnow is a free-lance writer based near Riverton, Wyo. He specializes in articles on equine research, and operates a ranch where he raises horses and livestock. He has authored several fiction and non-fiction books, including Understanding Equine Lameness and Understanding The Young Horse, published by Eclipse Press and available at www.exclusivelyequine.com or by calling 800/582-5604.
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