Bit & Bridle

Equine Mud Fever (Pastern Dermatitis)

Other Names

  • Scratches
  • Pastern dermatitis
  • Greasy heel
  • Dew poisoning
  • Cracked heel

What is Mud Fever in Horses?

Mud fever — properly known as pastern dermatitis — is a common, painful skin condition affecting the lower legs of horses, typically the pastern and fetlock areas. In severe cases it can extend up the cannon and lower limb. Despite the name, mud alone does not cause mud fever; rather, prolonged moisture and skin damage create the conditions for opportunistic bacterial and sometimes fungal infection to take hold.

The condition is most prevalent in autumn and winter in the UK when prolonged wet weather, muddy fields, and standing in sodden bedding all combine to compromise skin barrier function. However, mud fever can occur year-round, including in summer when horses stand in irrigated arenas or dew-soaked paddocks.

White-legged horses are particularly susceptible, as the skin under pink pigmentation is more sensitive and has reduced natural resistance. Heavy-feathered breeds such as Clydesdales, Shires, and Gypsy Cobs are also commonly affected, as the thick feathering traps moisture against the skin and makes early detection and treatment more difficult.

What Causes Mud Fever?

Mud fever is caused by a combination of skin barrier breakdown and opportunistic infection. The key organisms involved include:

  • Dermatophilus congolensis: The primary bacterial culprit. This unusual organism has characteristics of both bacteria and fungi and thrives in wet conditions. It is also responsible for rain scald on the body.
  • Staphylococcus species: Often found as secondary or co-infecting bacteria.
  • Dermatophyte fungi: In some cases, fungal infection (ringworm-type organisms) contributes to the picture, particularly in horses with persistent or treatment-resistant mud fever.
  • Chorioptic mange mites: Infestation with Chorioptes equi mites can cause lesions that resemble mud fever, particularly in feathered breeds. Always worth ruling out.

Contributing Factors

  • Prolonged exposure to wet and muddy ground
  • Frequent washing of legs without thorough drying
  • Repeated application and removal of boots, bandages, or wraps — particularly if put on damp skin
  • Alkaline soils, which affect skin pH and barrier function
  • Poor nutrition and compromised immune function
  • Photosensitisation — especially in white-legged horses exposed to plants such as St John’s Wort
  • Underlying skin conditions (such as vasculitis or immune-mediated dermatitis) can cause chronic or treatment-resistant mud fever

Signs and Symptoms

Mud fever typically presents in the following way:

  • Matted hair and crusting: The earliest sign is often a matted appearance to the pastern hair, with the skin beneath red and inflamed. Scabs form as the infection progresses — these may be yellowish, grey, or brown.
  • Skin cracking: The skin between the heel and pastern cracks, creating painful fissures that can weep serum.
  • Discharge: Lifting the scabs reveals moist, raw, inflamed skin underneath, sometimes with a purulent (pus-like) discharge.
  • Swelling: The pastern and lower cannon may become swollen and warm to the touch. In severe cases, significant limb oedema can develop.
  • Lameness: Mild to moderate lameness is common when infection is established, particularly on flexion of the fetlock.
  • Pain on handling: Affected horses are often very sensitive when the lower limbs are touched, making management and treatment challenging.

Diagnosis

Diagnosis is usually clinical, based on the characteristic appearance and location of lesions. However, in persistent or treatment-resistant cases, a vet may recommend:

  • Bacteriology and sensitivity swabs: To identify the specific organisms present and guide antibiotic selection
  • Skin scrapes and cytology: To check for mite infestation or unusual organisms
  • Biopsy: In chronic, treatment-resistant cases to rule out immune-mediated conditions such as vasculitis or pemphigus foliaceus
  • Blood tests: If systemic illness, photosensitisation, or an underlying condition is suspected

Treatment

Treating mud fever requires persistence and consistency. A half-hearted approach is one of the most common reasons cases drag on for weeks or months.

Step 1: Remove from Wet Conditions

This is non-negotiable. The horse must be stabled or moved to a dry environment. Continued exposure to mud and moisture will undermine any topical or systemic treatment. Clean, dry bedding (shavings or straw) is essential.

Step 2: Clean and Debride

Gently soften and remove scabs using a mild antiseptic wash (chlorhexidine scrub is commonly recommended). Scab removal is important — bacteria shelter beneath scabs and will continue to multiply if not exposed. This process is uncomfortable and may require sedation in very sensitive horses.

After cleaning, dry the legs thoroughly — a clean, dry towel, or a hair dryer on a low setting, is effective. Do not apply any cream or ointment to damp skin, as this traps moisture.

Step 3: Apply Topical Treatment

A wide range of topical products are available. Those with antibacterial and drying properties are most useful:

  • Antibacterial/antifungal creams (such as Sudocrem, hibiscrub-based preparations, or veterinary products such as Flamazine silver sulfadiazine cream for severe cases)
  • Barrier creams (Vaseline, Keratex Mud Shield, or similar) can be applied to healthy surrounding skin to prevent further moisture damage — but should not be applied directly over active infection

Step 4: Systemic Treatment if Necessary

In moderate to severe cases, oral or injectable antibiotics are required. Your vet will prescribe based on the case — commonly trimethoprim-sulphonamide (TMP-SMZ) or penicillin. A full course must be completed. In cases with significant limb swelling, short-term NSAIDs (bute or Danilon) help reduce pain and inflammation and allow the horse to walk and circulate blood flow to the legs.

Treating Feathered Breeds

In heavy-coated breeds, clipping the feathers is often necessary to allow effective cleaning and treatment. Many owners are reluctant to do this, but leaving thick feathering in place makes treatment significantly less effective and prolongs recovery. Once the infection is fully resolved, the hair will regrow.

Prevention

  • Manage the environment: Install drainage, hard-standing around gateways and water troughs, and rotate paddocks during wet months. Reducing standing time in churned mud is the single most effective preventive measure.
  • Dry before applying anything: If legs get wet, let them dry before putting on boots or applying barrier products. Boots put over damp legs are a common cause of mud fever.
  • Avoid excessive washing: Washing legs daily removes natural skin oils and compromises barrier function. Unless heavily soiled, allow mud to dry and brush it off. For horses that are being washed, ensure legs are dried fully.
  • Apply barrier cream proactively: Products like Keratex Mud Shield, Carr & Day & Martin Effax, or simple petroleum jelly applied to the pasterns before turnout can help resist moisture penetration in high-risk individuals.
  • Monitor daily: Check the lower limbs at least once a day during wet periods. Catching mud fever early — before scabs form and infection establishes — leads to much faster resolution.
  • Treat underlying issues: Address nutritional deficiencies, parasite burdens, or immune issues that may be reducing the horse’s skin resistance.

Prognosis and Recovery

Mild cases caught early typically resolve within 1–3 weeks with good management. Established infections with significant scabbing can take 4–8 weeks or longer, particularly in feathered breeds. Cases complicated by cellulitis, vasculitis, or persistent mite infestation require extended veterinary management and may recur seasonally.

Horses with chronic, treatment-resistant mud fever — particularly those with underlying photosensitisation or immune-mediated skin disease — may require specialist dermatological investigation and lifelong management.

When to Call the Vet

Contact your vet if:

  • The horse is lame or the lameness is worsening
  • There is significant heat, swelling, or lymphangitis (a cord-like swelling up the back of the leg)
  • Lesions extend above the fetlock
  • The horse does not respond to 2–3 weeks of diligent home treatment
  • Multiple limbs are severely affected
  • You suspect the lesions may be something other than straightforward mud fever

Frequently Asked Questions About Mud Fever in Horses

Should I remove the scabs when treating mud fever?

Yes — in most cases, scab removal is an important part of treatment. Bacteria live beneath the scabs, protected from topical treatments. However, the process can be painful. Soften scabs first with a warm, dilute chlorhexidine wash and allow it to soak before gently removing them. If your horse is very sensitive or the scabs are very thick, discuss sedation or pain relief with your vet before attempting debridement.

Can I turn out a horse with mud fever?

Ideally not, until the infection is resolved. If turnout is unavoidable, use turnout boots to protect the legs from further mud and moisture exposure — but make sure they are applied over dry, clean legs and are not left on for extended periods. Muddy, wet turnout will significantly slow recovery.

Why does my horse keep getting mud fever every year?

Recurrent mud fever usually comes down to a combination of environmental factors (paddock drainage, mud management) and individual susceptibility. White-legged and feathered horses are more prone. Underlying conditions such as photosensitisation or immune dysfunction can also predispose. Review your environmental management and work with your vet to rule out underlying causes if the horse is badly affected year on year.

Is mud fever contagious between horses?

Mud fever is not directly contagious in the way that strangles or ringworm is. However, the causative organism Dermatophilus congolensis can be present in shared environments, and good hygiene (not sharing brushes or boots between horses) is still advisable, particularly during outbreaks on a yard.