Scratches — also known as mud fever, greasy heel, or pastern dermatitis — is a common and frustrating skin condition affecting the lower limbs of horses, particularly the pastern and fetlock regions. The term describes a syndrome rather than a single disease, as multiple organisms (bacteria, fungi, parasites) and environmental factors can contribute. Scratches ranges from mild scabbing to severe, painful, swollen limbs that cause significant lameness. Chronic cases can be particularly challenging to resolve.

Overview

Pastern dermatitis develops when the skin barrier of the lower limb is compromised by persistent moisture, mud, abrasion, or irritation. Once the epidermis is damaged, opportunistic organisms invade, establishing infection and inflammation. The condition most commonly affects the hind limbs and is particularly prevalent in horses with heavy feathering (draft breeds), white/unpigmented skin, and those kept in wet, muddy conditions. Pastern dermatitis exists on a spectrum from mild dermatitis to severe cellulitis and lymphangitis.

Common organisms involved include:

  • Dermatophilus congolensis (same organism that causes rain rot)
  • Staphylococcus and Streptococcus species (opportunistic bacteria)
  • Dermatophytes (fungal organisms: Trichophyton, Microsporum)
  • Chorioptes equi (pastern mites, especially in feathered breeds)
  • Photosensitization (in horses with white legs exposed to certain plants)

Causes & Risk Factors

  • Wet, muddy conditions — Prolonged exposure to mud, standing water, or wet bedding
  • Heavy feathering — Draft breeds (Shires, Clydesdales, Friesians, Gypsy Vanners) trap moisture in leg hair
  • Unpigmented (white) skin — Less resistant to UV damage and irritation
  • Chronic moisture — Repeated washing of legs without drying, overwashing
  • Leg wraps and boots — Can trap moisture and heat against the skin
  • Poor hygiene — Dirty stalls, ammonia-soaked bedding
  • Immune suppression — Systemic illness, PPID
  • Mite infestation — Chorioptes equi causes intense itching and stomping that damages the skin
  • Vasculitis or immune-mediated disease — Leukocytoclastic vasculitis can mimic or underlie chronic pastern dermatitis

Symptoms

  • Mild — Redness, mild scaling, and small scabs on the back of the pastern
  • Moderate — Thickened, crusty scabs with raw, weeping skin underneath; hair loss; sensitivity to touch
  • Severe — Swollen, painful pasterns and fetlocks; deep fissures in the skin; foul-smelling discharge; lameness; proud-flesh-like granulation tissue in chronic cases
  • Stomping and rubbing (particularly if mites are involved)
  • “Grapes” or verrucous (warty) growths — In chronic, untreated cases, proliferative granulomatous tissue may develop (chronic progressive lymphedema in draft breeds)
  • Cellulitis — Hot, painful swelling extending up the limb if bacterial infection spreads deeper

Severe pastern dermatitis with limb swelling, lameness, or foul-smelling discharge requires veterinary attention. Deep infection or cellulitis can become a serious systemic problem if untreated.

Diagnosis

  • Clinical examination — Visual assessment and palpation of affected areas
  • Skin scraping — To check for Chorioptes mites, which are a common hidden contributor
  • Culture and sensitivity — Bacterial and/or fungal culture to guide antibiotic/antifungal selection
  • Skin biopsy — Recommended for chronic, non-responsive cases to identify underlying causes such as vasculitis, pemphigus, or neoplasia
  • Endocrine testing — ACTH testing for PPID in older horses with recurrent or refractory disease

Treatment & Medications

Successful treatment requires identifying and addressing the underlying cause, eliminating infection, and protecting the skin barrier:

Step 1: Clean and Debride

  • Clip hair from the affected area (essential in feathered breeds) to allow access to lesions and promote drying
  • Gently wash with chlorhexidine scrub (2%) or dilute betadine solution
  • Soften and carefully remove crusts (soaking for 10-15 minutes helps)
  • Pat dry thoroughly — moisture is the enemy
  • Repeat cleansing every 2-3 days initially, not daily (overwashing delays healing)

Step 2: Topical Therapy

  • Silver sulfadiazine cream (SSD, 1%) — An excellent topical antimicrobial for bacterial scratches. Apply a thin layer to clean, dry skin.
  • Desitin (zinc oxide) or petroleum-based barrier creams — Applied after antimicrobial treatment to protect healing skin from moisture
  • Ketoconazole or miconazole shampoo/cream — If fungal involvement is suspected
  • Lime sulfur — Effective for mixed bacterial-fungal infections
  • Topical corticosteroid (short course) — Betamethasone or triamcinolone cream to reduce inflammation and itching in acute flare-ups

Step 3: Systemic Therapy (When Indicated)

  • Trimethoprim-sulfamethoxazole — Oral antibiotic for moderate to severe bacterial infection or cellulitis
  • Dexamethasone — Short course of systemic corticosteroid for severe inflammation or suspected immune-mediated component
  • Ivermectin or moxidectin — If Chorioptes mites are identified on skin scraping. Multiple treatments may be needed.
  • NSAIDs — Phenylbutazone or firocoxib for pain and inflammation in lame horses

Step 4: Environmental Management

  • Provide dry footing (dry stall, well-drained paddock)
  • Minimize standing in mud or water
  • Clean, dry bedding (changed frequently)
  • Avoid overwashing legs; if legs get wet, dry them thoroughly
  • Use breathable leg wraps only when necessary and remove promptly

Prognosis

  • Mild scratches typically resolves within 1-3 weeks with appropriate treatment and environmental management
  • Moderate cases may take 4-6 weeks of consistent treatment
  • Chronic cases, especially in feathered breeds, can be lifelong management challenges
  • Identification and treatment of underlying mites, fungi, or immune-mediated disease dramatically improves outcomes
  • Recurrence is common if the environment remains wet and muddy
  • Chronic progressive lymphedema in draft breeds is a separate, progressive condition with a guarded long-term prognosis

Frequently Asked Questions

Why does my horse keep getting scratches even though I wash their legs every day? Frequent washing can actually worsen scratches by removing natural skin oils and keeping the area damp. Limit washing to every 2-3 days with a medicated shampoo, and always dry the legs thoroughly afterward. Barrier creams after treatment help protect the skin.

Should I clip the feathers on my draft horse’s legs? Yes, clipping is strongly recommended during treatment to allow access to the skin, promote drying, and enable topical medication to reach the affected tissue. Some owners of feathered breeds clip legs preventively during wet seasons.

Can scratches cause permanent damage? Chronic, untreated scratches can lead to scarring, permanent hair loss, and proliferative tissue changes (“grapes”). In severe cases, chronic lymphangitis can cause permanent limb thickening. Early, consistent treatment prevents these complications.

Is scratches contagious to other horses? The individual organisms involved (bacteria, fungi, mites) can be transmitted between horses through shared grooming tools, wraps, or direct contact. However, scratches itself is primarily a condition of environmental exposure and individual susceptibility rather than a highly contagious disease.

This information is for educational purposes only and does not replace professional veterinary advice. Consult your equine veterinarian for persistent or severe cases of pastern dermatitis.