Horse Skin Problems and Diseases

Rain Rot

Also known as rain scald, rain rot is a common equine skin condition medically termed dermatophilosis because it is an infection caused by the bacterium Dermatophilus congolensis. Certain horses are thought to be carriers of these normally dormant bacteria, and when chronic moisture and skin trauma occur simultaneously, rain rot can result.

Luckily for horse owners, rain rot is easy to identify. Known by its characteristic “paintbrush” lesions, the hair on a horse’s back and rump becomes crusty and matted in small clumps. Underneath these clumped bits of hair is raw, tender skin.

Once you’ve identified rain rot, here’s what to do:

1. 1. Bathe your horse gently with an antibacterial shampoo.
   2. Try to remove as many of the matted hair clumps as possible, but take care—this can be painful for your horse. In severe cases, sedation by your veterinarian may be required.
   3. After bathing, dry your horse completely and keep him in a dry place until the skin condition has healed, which can take a week or more. Dryness is imperative in the healing process, since moisture is required for the bacteria to proliferate.
   4. Most simple cases of rain rot can be treated with just a good shampoo and a dry environment, as described above. However, sometimes the lesions become infected with other bacteria. If your horse is particularly painful or you notice a foul smell or discharge coming from your horse’s skin, call your vet. Systemic antibiotics may be needed.

Scratches

Medically known as pastern dermatitis, scratches goes by many other common names that all mean the same thing, such as greasy heel, cracked heel and mud fever. This equine skin condition occurs at the back of the pastern and is characterized by swelling, hair loss, red, irritated skin, and the formation of scabs. This condition understandably causes sensitivity in your horse’s heel and can be severe enough to cause lameness.
While the true cause of scratches has yet to be determined, this skin disease is most commonly seen in horses that spend lots of time standing in wet or unsanitary conditions. Horses with feathers are predisposed to this disease, as long hair along the lower leg retains moisture close to the skin. Scratches usually affects two or all four feet.

Tender, raw heels are the featured characteristic of this disease. Here’s what to do if you see it:

1. 1. Like with rain rot, dryness and cleanliness are the keys to beating scratches. If your horse has feathers, the extra hair should be clipped away to allow adequate airflow to the skin.
   2. After clipping, if it is needed, wash the pastern area with an antiseptic scrub, such as 2 percent chlorhexidine. This not only cleans the skin, but also acts as a drying agent. Dilute iodine works well, too.
   3. During washing, remove the scabs. For some horses, this may be painful, so be careful and go slowly. If your horse is extremely sensitive, your veterinarian may have to administer sedation in order to properly clean the affected areas.
   4. After washing, completely dry your horse’s legs and then keep your horse in a dry environment while the skin is healing. This will require stall time if pastures are wet or muddy. If your horse is stall-bound, keep the stall as dry and clean as possible.

Hives

Hives is a common allergic reaction in the skin. It can be the result of your horse’s exposure to something his immune system is over-reacting to, such as an insect bite or sting, drug reaction, pollen, or other seasonal allergy.

Also called welts or (medically) urticaria, hives appear as raised, shallow bumps that can emerge anywhere on your horse’s body. They are most commonly seen along the neck, shoulder or abdomen. Hives can be itchy and warm to the touch, but most mild cases disappear on their own. The easy part of hives is identifying the condition. The hard part is often finding the cause, since allergies can sometimes have multiple sources.

If you notice hives on your horse, here’s what to do:

1. 1. Evaluate the severity by observing where the hives are on the body, how many there are, and how your horse is behaving. In mild cases, a horse won’t indicate that he is bothered, but more severe allergic reactions can be extremely itchy or worsen to cause swelling of your horse’s airways. Therefore you should also examine your horse’s breathing.
   2. If your horse appears content, think back to what your horse has been exposed to in the past 12 to 24 hours. Has there been any new medication, ointment, feed, supplement, tack, bug spray, shampoo, or even a change in bedding?
   3. Many mild cases of hives will go away on their own. If you don’t see resolution in the skin condition within six to eight hours, or if you notice that things are getting worse, call your veterinarian. Administration of a corticosteroid such as prednisolone usually helps eliminate the immediate itchiness. Some detective work may help you identify the cause so as to prevent hives in the future.

Sweet Itch

Sweet itch is a common seasonal skin disease that is actually an allergy to biting midges, also called “no-see-ums.” This condition most commonly occurs along the horse’s topline, around the mane and tail, as well as on the face and ears. It manifests in a range of signs that include scaly patches of itchy skin, scab formation, and hair loss in affected areas.

If you see your horse becoming itchy and miserable in the summer, here’s what to do:

1. 1. Treat the immediate skin reaction. This normally involves a veterinarian’s prescription for oral steroids for a short time. These drugs will help reduce skin inflammation and prevent itchiness. Preventing your horse from perpetually itching will then allow the skin to begin to heal.
   2. Reduce your horse’s exposure to biting midges. Since these insects feed primarily at night, stalling your horse during this time with a fan can help decrease the number of bites. Flysheets and spraying with an insecticide containing pyrethrin will also help.
   3. Establish an insect control plan at the barn to help your horse in the future. This includes proper manure management, adequate ventilation in the barn, and minimizing stagnant water.

Skin Cancer

Sarcoids and melanoma are two of the most commonly encountered equine skin cancers. Both types of cancer can range from fairly benign to invasive and destructive. While most sarcoids appear on the head, neck, or legs of a horse, melanoma occurs most commonly in gray horses around the perineum and elsewhere underneath the tail. Sarcoids can come in a variety of shapes and sizes, while melanoma is usually fairly uniform and distinct as a firm nodule or group of nodules.

Treatments for equine skin cancer vary based on what type of cancer is present, its location, and how invasive it is. However, in general terms, here are some guidelines:

1. 1. If you have a gray horse, make checking under the tail a regular part of your grooming routine. This way, you have greater chance of noticing something unusual earlier.
   2. For all types of horses, take the time during grooming to note any odd lumps or bumps anywhere on your horse’s body. If you notice something that appears painful, oozing, changing size, or is otherwise irritating your horse or concerns you, call your vet to come look at it.

Anna O’Brien, DVM, is a large-animal ambulatory veterinarian in central Maryland. Her practice tackles anything equine in nature, from Miniature Horses to zebras at the local zoo, with a few cows, goats, sheep, pigs, llamas, and alpacas thrown in for good measure.

This article originally appeared in the February 2016 issue of Horse Illustrated magazine. Click here to subscribe!