Terms: Pentoxifylline, ectoparasites (mites), bacteria, bloodflow, yeast, fungual dermatophytes.
Exudating – crusting, weeping, hair loss, erosions due to vasculitis (inflammation blood vessels), itching.
Differential diagnosis (causes) of lower limb dermatitis include:
- Photosensitivity of non-pigmented areas
- Irritant or allergic contact
- Infection from staphylococcus, dermatophiloss, malassezia (yeast)
- Immune mediated
Consequently, giving your veterinarian a complete history, including systemic and topical medications used, the examination, and diagnostics are of utmost importance. Diagnostics can include skin scrapings, skin cytology, and biopsy.
Environment can be predisposing or primary factors in equine pastern dermatitis, such as: bedding, pasture, sand, insect burden, moisture. Irritant contact dermatitis is commonly associated with chronic moisture such as muddy pastures and bathing without drying the pastern. Of course, chronic moisture predisposes to dermatophyte (fungal) infection as well, which can be contagious to people.
Symptoms include, swelling, scaling, loss of hair, crusting, exudate, may include ulcers due to vascuitis from secondary bacteria infection. Constant movement can produce cracks and fissures in the skin and can cause lameness and itching.
Bacterial infections associated with this syndrome are two primary organisms: staphylococcus aureus and dermatophilus congolensis which can involve crusting, secretions, and ulceration beneath scabs. Chronic moisture with trauma are required for these invaders. Immuno-compromised horses are more susceptible, thus, corticosteroids anti inflammatory use in the horse can be a predisposing factor. Fungal infection can be part of the cause for this dermatitis. The mites cause lots of itching and, or, stamping feet. Suspicion of the mites becomes greater if other horses in contact are affected.
Horses with white extremities are susceptible to photo-sensitization from ultraviolet rays. Contact photo-sensitization in the horse can be caused by exposure to clover pastures. Other causes of photo-sensitization can be ingestion of the St. John’s Wort, buckwheat, and rye grass. Photo-sensitization can also be a sign of liver problems.
Recommend veterinary consultation may involve diagnostic procedures like: skin scraping, microscopic examination with and without stain, specialized culture for fungal elements, and possibly biopsy for immune-mediated and cancerous lesions.
Predisposing factors include pastures with mud, water and sand.
- Dry stalls during wet weather.
- Turn out after morning dew dried.
- Avoid contact allergy by switching bedding, for example avoiding treated wood shavings.
- Clip hair to avoid moisture retention.
- If photo-sensitization is suspected avoid exposed to UV rays using wraps.
- Affected skin should be cleansed immediately after exercise using an antiseptic shampoo.
- If lesions are below the saddle, a towel or cotton sheets changed daily pay prevent spread.
- Consider disinfecting tack, blankets, saddle pads, etc. where relevant and create a changeable barrier between the horse and these items.
Use antibacterial shampoos such as benzoyl peroxide (2%) or chlorhexidine 2% (or other products). Shampoo, lather, let soak 10-30 minutes gently removing crusts, rinse and dry well. Repeat this for 1 week, then repeat 2-3 times weekly. This procedure will help greatly with the common secondary bacterial infection.
A product that can be applied as a wash/rinse or sprayed on left to dry daily is hydrogen peroxide (pure oxygen) addressing bacterial, fungal, and viral pathogens.
This product is safe for topical use on horses and all surfaces.
When lesions produce exudate, lime sulfer solutions can be used topically.
Systemic antibiotic therapy may be needed in severe cases (15-30 mg/kg every 12 hours): Trimethoprim sulfamethoxazole.
Discontinue antibiotic therapy in the horse immediately if any signs of diarrhea or colitis occur. Enrofloxacin 5mg/kg orally every 24 hours has been used successfully. Do not use Enrofloxacin in foals or growing horses! Procaine Penecillin G 22,000 IU/Kg intramuscularly twice daily for 7-10 days can be used to treat dermatophilosis infections. Please consult your veterinarian for the needed duration of these therapies. Remember, the horse is susceptible to colitis with the use of any systemic antibiotic.
Systemic antifungal therapy with Griseofulvin has little data to support its effectiveness; However, the author has used this drug with great success on severe skin infections caused by fungal elements for years. Ketoconazole, and fluconazole are also available for systemic antifungal treatment at greater expense.
Antiparasite therapy includes ivermectin 1% given orally at a dose of 300ug/Kg once weekly for 4 consecutive weeks. Topical pour on Eprinomectin (500mg/Kg) once weekly for four applications is effective against mange mites. Topical treatment include permectrin, selenium sulfide shampoo followed by lime sulfer (6oz per gal.) sponged on every 5 days for 1 month. Environmental decontamination is important as well.
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Source: “Equine Pastern Dermatitis”. Equine Dermatology. December 2013. (pp 577-588, Author Anthony A. Yu, DVM, MS)