It’s that time of year again, when winter’s thaw meets spring showers to create epic mud season. And with mud season comes horses, blankets and turnout boots caked in the stuff. But it’s not just messy; for some horses it also brings pastern dermatitis or “mud fever.”
Mud fever, also known as scratches, is a common skin condition that affects the lower limbs, particularly the back of the pastern and heels. It is typically caused by prolonged exposure to wet, muddy environments (pastures and paddocks, we’re looking at you), which creates ideal conditions for bacteria and fungi to thrive.
Mud fever can present as scabs, inflammation, hair loss and oozing lesions, and may cause discomfort or even lameness if left untreated. While the primary culprit is usually the bacterium Dermatophilus congolensis, other organisms and environmental factors can also contribute.
Understanding and addressing the root causes of mud fever is key to maintaining a horse’s health and comfort. To help us with this, we turned to Dr. Kate Robinson, an associate veterinarian at McKee Pownall in Ontario. And as with any health issue or treatment, owners should always seek advice from their regular veterinarian before treating their horse.
HORSE CANADA: What is mud fever?
DR. KATE ROBINSON: Mud fever is an inflammatory condition of the distal limb involving the superficial layers of the skin. It is most common on the palmar or plantar (back) surface of the pastern region and typically affects white legs (but any colour may be affected). Affected limbs develop areas of crusted/oozing lesions that are often red and painful. The skin may crack and become thickened in more chronic or severe cases. Lesions can spread around the front of the limb and go higher up; this may be a sign of a more severe disease called pastern leukocytoclastic vasculitis (PLV).
Mud fever is a multifaceted disease with bacteria, fungi and viruses being implicated as contributing etiological agents. As well, in some cases sunlight or photosensitization may play a role. And excess moisture or abnormal wet/dry cycling may also contribute (think dew on morning grass). Lastly, there may be allergic or environmental factors at play, as some horses will repeatedly develop mud fever for years and then stop having outbreaks upon moving to a different farm.
Mud fever or ‘scratches’ can cause discomfort and even lameness if left untreated. (Dr. Trisha Dowling photo/Canadian Horse Annual)
How is mud fever treated?
Because multiple etiological agents may be involved, multiple treatments and/or a combination treatment may be required.
For mild cases, I recommend clipping the hair from the region to allow more accurate application of topical treatment. Gently cleanse the area with a mild disinfectant, such as blue chlorhexidine solution. If the horse allows, gently remove any crusts that soften and come off easily. Some horses are quite painful with mud fever (regardless of severity) and require sedation for treatment. After cleansing and removing softened crusts, dry the area and apply a generous layer of Penaten® ointment for mild cases. This will be repeated at least once a day.
More severe cases, chronic cases or cases not responding to gentler treatment may require a prescription ointment. Often these are compounded ointments that contain a soothing zinc oxide, steroid to help control inflammation, antibiotic and antifungal medications. Further to that, I will sometimes prescribe a course of systemic (usually oral) anti-inflammatories (NSAIDs or steroids) and antibiotics in particularly tough cases, with the idea of treating the skin from the inside and the outside. Rarely, hospitalization and specialized care may be required for resolution.
It may be a good idea to keep horses inside for a few days at the beginning of treatment to decrease exposure to sun and moisture, as well as to keep the area clean. Alternatively, wraps/bandages may be placed over the affected area, but again become problematic when wet/dirty.
Dr. Kate Robinson.
How can mud fever be prevented in the first place?
Prevention can be difficult, as so many factors may be involved. In horses where sunlight and/or excess moisture are identified as factors, efforts should be made to avoid them. Altered turnout schedules and use of boots or wraps may be helpful, although boots/wraps become useless when wet and trapping moisture against the skin.
Otherwise, regular grooming to remove mud and debris and allowing the skin/hair to dry may be helpful. Use of a barrier cream such as Penaten® may be protective in horses who have previously suffered from mud fever, but is not recommended for horses with no history of the disease.
Maintaining paddocks and turnout so that they are as dry and clean as possible can go a long way in prevention. This may mean adding material (bedding, pea gravel, mats) to build up lower areas and/or help keep them drier.
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For more tips on reducing mud in paddocks, read “Managing Mud: Solutions for Swampy Paddocks”
