Mud fever (pastern dermatitis or equine pastern cellulitis) is a common and welfare-significant skin condition affecting horses kept in wet, muddy conditions. Though often perceived as minor, severe cases cause significant pain and lameness.
Mud fever results from disruption of the skin barrier in the pastern region, allowing opportunistic infection by bacteria (primarily Dermatophilus congolensis and secondary gram-negative bacteria), fungi, and in some cases photosensitising plants. Prolonged wetness softens the skin, abrasion from grit and mud further damages the barrier, and subsequent bacterial colonisation causes inflammation. White-limbed horses are more susceptible — pigmented skin has greater barrier resistance.
Early signs: matting of pastern hair, crusty scabs at the back of the pastern, mild swelling. The horse may be mildly foot-sore. Moderate to severe cases: extensive scabbing with exudative, painful lesions, significant swelling of the pastern and fetlock, lameness that may be marked in severe cases, and reluctance to bear weight. Extensive cellulitis from secondary bacterial infection can spread up the limb. The welfare impact ranges from minimal discomfort in early mild cases to significant pain in severe established cases.
Environmental management: Addressing the underlying cause — preventing prolonged pastern wetness — is essential for both treatment and prevention. Moving horses to hard standing (concrete, rubber matting) or indoors during wet weather prevents continuous reinfection. Where turnout on wet pasture is unavoidable, rotating paddocks to rest wet areas and using track systems reduces mud exposure.
Wound care: Affected areas should be gently clipped (removing hair allows better treatment access and inspection), scabs softened with a mild antibacterial wash and removed (this is briefly painful but necessary for treatment access), and the lesion dried thoroughly. Barrier creams applied daily protect healing skin from further moisture exposure.
Medical treatment: Mild cases often resolve with topical treatment and improved environment. Moderate to severe cases require systemic antibiotics (penicillin-based for Dermatophilus, broad-spectrum for mixed infections) and anti-inflammatory medication (NSAIDs) for pain relief and to reduce swelling. Cases not resolving with standard treatment warrant skin biopsy and culture to identify resistant organisms or underlying conditions (chorioptic mange, photosensitivity, pemphigus).
Some horses develop chronic, recurrent mud fever despite appropriate management, suggesting underlying predisposing factors. Chorioptic mange (feather mite infestation, particularly in heavy horses) causes similar lesions and predisposes to secondary bacterial infection. Vasculitis, photo-sensitisation, and immune-mediated conditions are rarer causes of persistent pastern dermatitis requiring veterinary investigation.
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