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Unearthing the Root Cause of Equine Pastern Dermatitis

August 27, 2021 4 min read

Unearthing the Root Cause of Equine Pastern Dermatitis

Equine pastern dermatitis. Greasy heel. Dew poisoning. ScratchesMud fever. No matter what you call it, pastern dermatitis is an uncomfortable and aggravating skin condition that can cause lameness and cellulitis if left untreated. 

Symptoms include:

  • Lesions
  • Pus
  • Hair Loss
  • Skin Thickening
  • Inflammation
  • Oozing Sore

What makes management of equine pastern dermatitis (EPD) so frustrating to horse owners and veterinarians, is finding what caused the condition in the first place. EPD is more a collection of diseases than a diagnosis in itself. The word “dermatitis” is defined by the Mayo Clinic as a skin irritation. So essentially, equine pastern dermatitis is a skin irritation of the horse’s pastern. Because the diagnosis itself is not very useful in terms of management, it’s important to get to the root cause of the issue in order to get your horse back to full health.

How to Find the Root Cause


Step 1: Diving into the History

Dig deep into your horse’s history with your vet. Knowing what month the issue began, what treatments you have already tried (including home remedies), and a detailed description of your horse’s environment is key. The cause of your horse’s equine pastern dermatitis could be right there in his past. For example, if EPD appears seasonally, it could be related to an allergy of a specific plant, pollen, or insect. Some home remedies can actually be quite bad for the horse’s skin and make the issue worse. Be thorough in telling your vet what you’ve already tried to avoid reactions between substances.

To some degree, certain breeds of horse are more susceptible to pastern dermatitis. For example, the heavy feathering on the legs of draft horses or friesians makes them more susceptible. However, horses with white legs are also prone to skin irritation, as well as horses with metabolic disorders. Examining your horse’s medical records will help you find and manage these genetic predispositions.

Step 2: Examine Your Pasture

Has your horse been grazing on clover pastures, or exposed to St. John’s Wort, Buckwheat, and Ryegrass? Have they been taking any medications such as phenothiazine, thiazides, sulfonamides, and tetracycline? These “photoproducts” cause a molecular reaction when UV rays reach the skin. This reaction, known as photosensitization, results in inflammation and skin irritation. If you believe your horse is suffering from photosensitization, take a look at their muzzle. Dermatitis from photosensitization impacts the muzzle and outer extremities

Besides examining your horse’s environment, running blood work is another way to diagnose photosensitization, as well as a range of metabolic disorders that could predispose your horse to EPD. 

Step 3: Look for Mites

Equine pastern dermatitis could also be a reaction to mites. Mites cause several different types of mange in horses, most commonly near the pastern due to the presence of feathers. Horses with dermatitis from mites stomp their feet, rub one fetlock against the other, or rub the leg on various objects.  


A superficial skin scraping is a relatively non-invasive way to rule out mites as the cause of your horse’s dermatitis. To confirm mites are the culprit, your veterinarian will use a dull blade to scrape dander and crusts off your horse’s pastern and into a container. The collected debris will be examined under the microscope for mites. 

Step 4: Review Your Stable Management

One cause of pastern dermatitis is consistent exposure to moisture and dirt. A dirty stall means your horse is lying down in urine-soaked bedding, while a pasture with poor-drainage could mean your horse is standing in mud all day. In both of these instances, your horse’s skin barrier is weakened by the chronic dampness and more susceptible to skin irritation. Before taking more invasive measures to find the root cause of your horse’s pastern dermatitis, evaluate how you manage your horse’s stable and find ways to eliminate exposure to additional moisture. 

Step 5: Biopsy and Culture

If you haven’t found the cause of your horse’s dermatitis by this step, it might be time for a biopsy. A biopsy and culture tells you if the condition is related to Staphylococcus aureus and

Dermatophilus congolensis bacteria. Consider the appearance of the dermatitis before biopsying, as according to Dr. Anthony Yu, “lesions seen with D. congolensis infection typically are crusting and exudative and when crusts are removed the skin is ulcerative.”

Why the Pastern?

Why is the pastern so susceptible to equine pastern dermatitis? The skin and hair covering the pastern is the same as every other part of your horse. However, it’s unique location means that it is constantly exposed to mud, urine-soaked shavings, manure, rocks and sticks. The back of the horse’s heel creates a nice natural “cup” compared to the smooth slope of the back where water and possible chemical irritants (like fly spray) will linger for a longer period of time. All of these factors combine to create the ideal environment for skin irritation.

Managing Equine Pastern Dermatitis

Figuring out the root cause of your horse’s EPD can take time. While you and your vet work to find the cause, there are a few basic steps you can do to help your horse. 

First, clipping the pastern will help you to keep it dry and clean. The long hairs can trap moisture, dirt, and mites close to the skin, so removing it will provide some relief. Second, check the area closely at least once a day to monitor for any new symptoms or growth of proud flesh. Pay close attention to the other legs as well to catch any spread of the dermatitis as early as possible. Third, use an equine barrier cream to avoid any cracking or fissuring of the skin and start the healing process. 

Zarasyl equine barrier cream can be easily applied by a horse owner, barn manager, or stable hand. Non-irritating and non-toxic,  Zarasyl is odorless, non-volatile, water miscible, and chemically stable with a competition and race-day safe formula. This equine barrier cream provides sustained delivery of orthosilicic acid to the skin, which is the bioavailable form of silicon associated with healthy connective tissue growth.

If your horse is struggling with equine pastern dermatitis, try managing it with Zarasyl equine barrier cream. Buy your tube of Zarasyl here.