Watch out for 8 common equine skin diseases

Here's what you need to know about those skin lumps, bumps and bald patches on your horse that you can probably handle on your own.
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Here's what you need to know about those skin lumps, bumps and bald patches on your horse that you can probably handle on your own.

There it is again---that strange-looking bump, or scruffy patch, or bald spot on your horse's skin. It looks harmless, and it doesn't bother your horse when you touch it. But it just won't go away.

Photo © EQUUS Magazine. All Rights Reserved.

Photo © EQUUS Magazine. All Rights Reserved.

Is it something you can safely ignore, or do you need to treat it? The answer depends on whether the spot or bump in question is caused by a bacterial, fungal or viral infection, an insect bite, sunburn, allergic reaction, bruise, abrasion or any number of assaults the world can throw at a horse.

The good news, says William H. Miller, VMD, professor of dermatology at Cornell University, is that many equine skin diseases and conditions are not very serious. In fact, some issues are considered merely cosmetic and may be left untreated, and in many cases, a knowledgeable horse owner can safely handle the situation on their own.

But there's a catch: In order to treat a condition effectively, you need to know for sure what it is, and some issues that stem from completely different causes can look remarkably similar. Just reaching for your favorite ointment and applying it to the skin can do more harm than good. Heavy salves like Vaseline, for example, can plug hair follicles, and many homemade remedies can irritate skin.

What's more, says Miller, persistent skin problems are rarely just skin-deep. "Skin diseases can be indicative of a compromised immune system brought on by poor nutrition, age or other disease," he explains. So no matter how basic your horse's skin problem may seem, if it doesn't respond to treatment or continues to recur, talk to your veterinarian. Not only can she confirm the identity of the issue, she will help you develop a treatment plan that may include dietary and management changes and possibly systemic drugs in addition to topical treatments. And in any case, if you're unsure what you're seeing or how to handle it,
it's always best to consult with your veterinarian.

But if you're looking at one of these eight common equine skin ailments, especially if you notice them early, you may be able to manage them safely on your own.

1. Rainrot (rain scald)

  • Appearance: scabby crusts that form raised bumps with upright tufts of matted hair. The crusts form on parts of the body that are chronically damp---often along the topline and where rain runs off down the barrel, shoulders or hindquarters, but also on the lower legs or faces of horses who regularly stand in mud or graze tall, wet grass. Over time, the crusts peel off, leaving small, round bare spots; pus may also be seen under newly sloughed scabs.
  • Causes: Rainrot is a bacterial infection. The causative organism, Dermatophilus congolensis, can reside on the skin without causing trouble, but it multiplies rapidly in a moist environment. If the bacteria find a break in the skin, whether a small wound or insect bite, an active infection can develop. Anything that compromises a horse's immunity---advanced age, malnutrition, illness---can make him more susceptible to the infection, as can having a heavy winter coat, which tends to trap moisture against the skin.
  • Do I need to treat it? Yes. Rainrot is uncomfortable, if not painful, for the horse, and it can cause unsightly patches of hair loss.
  • Treatment: First remove the horse from wet conditions and place him in a living arrangement where his coat can dry out thoroughly. A variety of anti-microbial shampoos and disinfectant rinses are available over-the-counter that are labeled for use on rainrot infections; the horse's coat will probably need to be treated daily for at least a week. The specific duration of treatment depends on the product being used and the severity of the infection. Spot treating may be effective if only a small area is affected; otherwise, giving the horse a full bath may be advisable. Picking off loose scabs may help them heal faster, because exposing the bacteria to air helps to kill them, plus it will enable topical treatments to penetrate further. But do not remove scabs if they are still tight and pulling on them causes the horse pain. Call your veterinarian if an infection fails to improve after a week, despite treatment. She can make sure your horse actually has rainrot, rather than another similar condition, and may prescribe a topical medication or oral antibiotics, especially if a secondary infection has set in.
  • Prevention: Provide dry areas that turned-out horses can retreat to in wet weather and keep your run-in shed's roof in good shape. Waterproof blankets and light sheets can also help keep pastured horses dry; just make sure their coats are not damp when you put them on. Groom often, both to clear away mud or dirt, which can hold moisture against the skin, and to spot the infection in its earliest stages. Disinfect all blankets and equipment that came in contact with an infected horse before reuse.

2. Ringworm (fungal dermatitis)

  • Appearance: rounded hairless patches with crusty, scabby skin. The lesions are most common on the face, neck, shoulders, chest or under the saddle or girth, but they can appear anywhere on the body. The affected areas may be sore or itchy, but they often cause no discomfort, and the horse may appear otherwise healthy.
  • Causes: Despite the name, ringworm is a fungal infection, which can be caused by several organisms, usually members of the Trichophyton or Microsporum families. The fungi, called dermatophytes, consume keratin, the protein that forms the structure of hair and epidermal skin cells. The fungi can survive for months in the environment, on tack or fences, and they can be carried on the skin for up to three weeks before signs of infection are evident---during this time, the fungi can be easily spread to other animals, and sudden outbreaks may affect every horse in a herd.
  • Do I need to treat it? Yes. Left untreated, the lesions will continue to grow and spread. Although infections might heal eventually on their own, the horses would be highly contagious until they do.
  • Treatment: If you suspect ringworm, immediately isolate the affected horse from all other animals, including cats and dogs as well as other livestock. Clipping the hair around the lesions and removing scabs and crusty material as much as you can without causing the horse pain will reduce the organisms' food source. Several over-the-counter antifungal medications, as well as some human dandruff shampoos, may be effective against ringworm, but you may need to try several products to find one that works best for your horse. First clean the area with a general antifungal antiseptic, such as chlorhexidine, then dry thoroughly before applying an antifungal ointment or medication. Repeat the treatments until the infection is resolved. Exposure to air and sunshine will also help kill the fungi. Call your veterinarian if the lesions continue to spread or the horse's skin does not appear to be healing after a week. She can confirm that the infection is ringworm by scraping off a few skin cells and examining them under a microscope for the presence of fungal spores. If the case is severe or if you are handling many cases at once, your veterinarian may prescribe oral medications that can be used in combination with the topical washes. • Prevention: Keep separate tack, equipment and grooming supplies for every horse in your care, and do not share with others at shows or events. Quarantine new horses brought to your farm for at least two weeks to make sure they aren't carrying ringworm or other contagious diseases. In the case of an outbreak, clean and disinfect any tack or equipment as well as wash stalls and fences in communal areas that other animals may have had contact with. Use a power washer to get disinfectant into all the crevices. Remember that people can get ringworm as well as all your other animals, including cats and dogs. Always wear gloves when handling infected horses and exposed equipment.

3. Warts (papillomas)

  • Appearance: raised gray or pink cauliflower-like growths that are usually fairly small, not much bigger than peas. They may appear singly or in clusters, most commonly on the muzzle or around the eyes but also occasionally on the ears, genitals and lower legs. The growths do not appear to cause any pain or discomfort.
  • Causes: Warts are caused by the equine papillomavirus, an organism that can survive on skin, equipment and structures for weeks. Younger horses, under 3 years of age, are more susceptible, although warts can appear in adults.
  • Do I need to treat it? No. The warts are harmless, unless they are inhibiting the horse from eating, blinking or moving or they are interfering with tack.
  • Treatment: Left alone, the warts typically shrink and disappear, leaving no scars, over the course of about four months as the young horse's immune system develops. They are likely to persist for a year or more when they appear in older horses. Warts that need to be removed can by excised with laser or cryosurgery, but these procedures may leave scars. Drugs that stimulate immunity may also be helpful. If warts do not go away on their own, have your veterinarian examine them; other diseases and conditions, including some sarcoids, can look very similar to papillomas.
  • Prevention: Isolate affected horses from others, especially younger ones. Disinfect any shared tack or equipment.

4. Aural plaques (papillary acanthoma, ear papillomas)

  • Appearance: flat, crusty, raised white lesions inside the ears; underneath, the skin may be pink and sensitive. Aural plaques usually cause no pain and are considered to be just a cosmetic problem. But biting flies may irritate the lesions, and some horses may begin to resist bridling or having their ears handled. Both ears are likely to be affected. They are not likely to shrink or go away on their own.
  • Causes: Aural plaques are caused by an equine papillomavirus that is thought to be spread by biting flies, such as the blackfly, that target the ears. The plaques may appear in horses of any age or breed.
  • Do I need to treat it? No, unless the plaques are bothering the horse.
  • Treatment: Most horses resent having the plaques physically pulled off, and doing so can inflame the ears and make the problem worse. If the plaques are causing ear sensitivity, your veterinarian may prescribe a course of treatment with a topical cream containing imiquimod, a drug that stimulates a localized immune response in the ear and helps diminish the lesions.
  • Prevention: Take precautions to protect your horse against biting flies, especially blackflies. Use fly spray, and outfit your horse with a fly mask that includes ear coverings. Also use ear covers that can be worn with a bridle, especially if you ride in wooded areas near water. Stable your horse at dawn and dusk, when blackflies are most active.

5. Primary seborrhea (dandruff)

  • Appearance: Seborrhea can be dry or oily. In the dry form, small flakes of skin appear routinely, usually at the base of the mane and tail, and sand-like flecks may appear on the girth area or anywhere sweat accumulates. Oily seborrhea causes large, waxy crusts, often on the elbows, hocks or lower legs; when peeled off, these may leave hairless patches up to several inches in diameter. Dandruff sometimes causes a fetid odor, but the horse is not usually itchy or in pain.
  • Causes: Heredity plays a significant role in cases of primary seborrhea, and it is more common in Arabians and Thoroughbreds. In affected individuals, dandruff is likely to be a lifelong issue. Please note, however, that primary seborrhea looks just like secondary seborrhea, which can also be either oily or dry. The biggest difference is that secondary seborrhea develops in horses who had not previously experienced the condition, although the onset can be very gradual. Secondary seborrhea is a sign that can accompany several potentially serious illnesses, including liver or intestinal disease.
  • Do I need to treat it? No, but most people prefer to do so for aesthetic reasons. Consult your veterinarian if your horse develops seborrhea or if a mild case seems to be getting significantly worse with no obvious explanation.
  • Treatment: Primary seborrhea is not curable, but it can be managed. A number of antidandruff shampoos are available that, when used as directed, can dissolve flakes and loosen oily scales. It's best to choose products formulated for use on horses; human products can be too harsh. Gentle scrubbing with a soft- to medium-bristled brush can help remove crusts. If you have difficulty controlling a stubborn case, talk to your veterinarian, who may recommend other topical medications. She may also suggest performing diagnostic work, such as blood tests, to rule out other causes. Secondary seborrhea is likely to clear up when the underlying disease is treated.
  • Prevention: Regular grooming stimulates circulation and natural oil production that help keep the skin healthy and clean. Feeding vegetable oils, especially omega-3 fatty acids, and supplements that contain biotin may also help promote healthier skin. Talk to your veterinarian or an equine nutritionist before making changes in your horse's diet.

6. Eosinophilic granuloma with collagen degeneration (nodular collagenolytic granuloma, nodular necrobiosis, or simply nodules)

  • Appearance: distinct, firm nodules about the size of a dime or smaller, found usually in the neck, back and withers. Several small nodules may cluster together to form what appears to be a larger lump. The skin above is normal, with no hair loss, and the nodules do not contain pus. The bumps can occur in horses of any age, breed or gender. They usually are not painful or itchy, unless they've been irritated by rubbing. Over time, they may mineralize, which makes them feel harder.
  • Causes: The nodules are caused by the breakdown of collagen, the protein that forms the structure of connective tissue, in the middle layer of the skin. Why this happens is not fully understood, but the inciting event is believed to be hypersensitivity, when the immune system overreacts to the presence of some allergen and creates a "mass" to contain it. Allergic reactions to insect bites are thought to be the most common cause of these nodules, but injections with silicone-coated needles, minor scratches from body clipping and other traumas may be responsible in some cases.
  • Do I need to treat it? No, the nodules are harmless, unless they are interfering with tack or continuing to grow in size because the horse is rubbing them.
  • Treatment: Your veterinarian can inject corticosteroids into the nodules to shrink them. If the nodules are still present after three or more injections, which are usually given at two-week intervals, she may suggest surgical removal. The nodules become more difficult to treat medically once they have calcified, so some veterinarians may recommend more aggressive treatment earlier after they appear.
  • Prevention: Take measures to protect your horse from biting flies, including the use of fly sprays and turnout sheets. If your horse has developed nodules at injection sites, ask your veterinarian to use noncoated needles for future injections.

7. Mange

  • Appearance: small, round bumps at first, soon followed by bald spots, with scaly, thickened skin, usually on the lower legs of draft horses with heavy feathering, although any horse can be affected. In more serious cases the skin may be rubbed raw and show signs of secondary infections. Mange causes itching, and horses will rub, stamp and bite at their legs. In rare cases, mange may appear on other parts of the body.
  • Causes: Mange is a parasitic infection caused by several species of tiny mites that can barely be seen by the naked eye. The most common form that occurs in horses in the United States is chorioptic mange, caused by the mite Chorioptes equi, which typically affects the lower legs of horses with feathering. Although rare, horses may also develop psoroptic mange (Psoroptes equi), which produces lesions under the mane and tail, under the jaw and in the groin and armpits, and demodectic mange (Demodex equi), over the face, neck and shoulders.
  • Do I need to treat it? Yes. Not only is mange uncomfortable for the horse, it can cause permanent thickening and scarring of the skin that can impede the movement of the pastern joints.
  • Treatment: A number of topical antiparasitic products can be effective against mange---look for products that contain lime-sulfur solutions, organophosphates or permethrins, which can be applied by spraying, sponging or dipping the leg. Administering oral ivermectin or moxidectin may also be helpful in some cases. Treatments may need to be repeated three or four times at 12- to 14-day intervals. Clipping the legs will help the topical treatments reach the skin but may not be necessary in all cases, especially if the infection is still mild.
    Call your veterinarian if the infection is severe or does not respond to treatment. She can examine skin scrapings under a microscope to confirm the presence of the mites, and she may suggest an alternative treatment. Oral antibiotics may be necessary to treat secondary infections.
  • Prevention: Mites usually are passed directly from horse to horse, so do not allow your horse to have contact with others at shows or events and quarantine newcomers on your farm, especially if they have visible bald areas that appear to be itchy. Some horses can carry the mites without showing signs of infection and can be a source of recurrence after other horses are treated. If you have an outbreak, it's a good idea to treat all horses who have been in contact with the ones affected and change out all of the stall bedding used by affected horses.

8. Lice (pediculosis)

  • Appearance: hair loss from rubbing, usually appearing first on the shoulders and neck, as well as on the head and the base of the mane and tail. Affected areas are intensely itchy and may also have abrasions and scabs from rubbing and possibly secondary infections. Flattened insects up to two to four millimeters long may be visible if the hair is parted and the skin examined in good light. Pale, translucent eggs may be attached to nearby hairs. The horse is also likely to be generally unthrifty and in poor health. Lice infestations tend to be more severe during the winter months but can occur at any time of year.
  • Causes: Two types of these parasitic insects infect horses: Chewing lice (Damalinia equi) feed on sloughed-off dead skin cells; these are more likely to affect the neck, flanks and the base of the tail. Biting or sucking lice (Haematopinus asini) feed on blood; this species prefers longer hair and may be found under the forelock and mane, the tail and on the pasterns of long-feathered horses. Both types cause skin irritation and itching.
  • Do I need to treat it? Yes. Not only is a lice infestation extremely uncomfortable for the horse, severe cases can cause anemia.
  • Treatment: Several types of products---permethrin sprays and wipe-ons, insecticidal powders and shampoos---are effective against lice. Read and follow label instructions and precautions carefully. Many treatments need to thoroughly coat the skin to be effective, but some products may irritate small cuts and abrasions. Oral ivermectin may be effective, but only against the biting lice. Because the insecticides will not kill eggs, the treatment needs to be repeated in two weeks to eliminate newly hatched adults.
  • Prevention: Lice can be passed directly from horse to horse, as well as via shared tools and equipment. Isolate affected horses as well as those who have been exposed to them.
  • Louse eggs that detach from the horse's coat can hatch and re-introduce the infestation, so it is important to clean and sterilize any tack and equipment that was used on the affected horse. Clean brushes and small tools with an insecticide, or boil items that will not be damaged by heat. Pads and blankets can be sterilized by machine washing and drying at a high heat setting. Also spray or scrub down stall walls or paddock fences and change the bedding.

Your horse's skin is his first line of defense against most of the bugs and microbes in his world, and he will most likely experience his fair share of minor ailments over the course of his lifetime. By learning what to do, what not to do, and when to call the veterinarian, you can do your part to keep his skin healthy and strong.