Pastern dermatitis, more commonly known as “Greasy Heel” or “Mud Fever” (“Scratches” in the USA), is an inflammatory condition of the skin involving the lower limbs. It is a very common annoyance for horses (and hence those that care for them) especially in the wetter months.
Often as painful as it is unsightly and difficult to manage, clinical signs can range from inflammation, hair loss, scabs, cracked and ulcerated skin, to granulation tissue, discharge and generalised swelling of the lower limbs and associated lameness. It can often involve multiple limbs with non pigmented skin more adversely affected than dark haired limbs.
They key to preventing this condition is understanding the underlying risk factors. Most cases are characterised by disruption to the healthy skin barrier, excessive exposure to moisture and opportunistic infection. The key to treating this condition involves a multi-pronged, treatment plan.
Breaking Down the Barrier
The skin is normally an effective barrier against surface pathogens such as bacterial, fungal or parasitic organisms. However, when there is trauma to the skin, this barrier is easily breached by such pathogens.
The most common causes of skin trauma to the pastern area are:
- Constant wet conditions ie wet long grass.
- Overley excessive washing of the legs.
- Wet abrasive conditions eg constant exposure to mud, poor stable hygiene etc.
- Mild repetitive trauma eg rubbing caused by bell boots, overreaching etc.
- Clipper rash.
- Insect bites.
- Contact irritants eg shampoos, chemicals, plants, bedding etc.
Opportunistic Infections: Invading Pathogens
Once the skin of the pastern area has been damaged, ubiquitous surface pathogens can then invade the skin. The resulting secondary infections may be caused by bacterial, fungal or parasitic pathogens. It is this resulting opportunistic process of infection that causes the clinical signs associated with Greasy Heel/Mud Fever. Additionally, immune-mediated conditions can mimic Greasy Heel/Mud Fever which explains why some rare cases are seemingly refractory to treatment.
The most common pathogens implicated in cases of Greasy Heel/Mud Fever are:
- A bacterial infection of the skin surface (superficial bacterial pyoderma)
- Staphylococcal spp. vey common
- Dermatophilus congolensis less common on pasterns but will be seen if there has been a previous problem with “rain scald” on the property.
- Chorioptic mange is a major differential for any pastern dermatitis, especially in well feathered breeds, that is caused by a mite. It is often characterised by foot stamping and biting as such infestations can cause itchiness (pruritis).
Less common causes of Greasy Heel/Mud Fever:
- Fungal Infection. Dermatophytosis (better known as ringworm) can occur in the pastern region.
- Environmental mites (eg from chickens sharing the same environment).
- Helminth dermatitis Strongyloides westeri larvae will occasionally invade the skin, typically under moist, unhygienic conditions. The muzzle is also classically affected and the lesions are typically pruritic (itchy).
Rare causes of Greasy Heel/Mud Fever:
- Liver disease.
- Pemphigus foliaceous.
- Coronary band abnormalities.
- Proliferative hyperplastic pastern dermatitis of draught horse breeds.
Prevention- Easier Than Cure.
Minimising skin trauma to the pastern region is your primary defence against Greasy Heel/Mud Fever.
- Ensure that lower limbs are not constantly exposed to water and abrasive agents, to this end consider moving water troughs and feed bins regularly to avoid high traffic created mud patches. Move horses out of mud prone paddocks and long grass during wet weather.
- Keep the pastern region as dry as possible to prevent the skin from becoming macerated as a result of constantly being wet. (Not unlike the skin our own hands when they are constanly exposed to water).
- When clipping horses, take extra care so as to prevent trauma to the underlying skin (clipper rash), consider not clipping legs or feathers which can help facilitate drainage.
- Maintain good stable hygiene.
- Vigilently check that protective gear is not rubbing (eg bell boots).
- Avoid the use of chemicals (purple sprays, sulfur products, methylated spirits, bleach, sump oil etc!) which can irritate and cause further skin damage.
- When washing your horse, thoroughly rinse off any shampoo residue and dry the limbs gently but thoroughly. Use only good quality horse shampoos and conditioners.
- Inspect and palpate the pasterns regularly for changes in skin health such as inflammation, scabs and wounds. Treat any abnormalities promptly, especially during wet conditions. Early intervention is key.
- Maximise skin surface health. Apply moisturisers to dry, scaley skin. Sorbolene is beneficial but be mindful that tubs of cream can easily become contaminated.
- Avoid sun damage.
10 Steps to Effective Treatment.
Effective treatment of Greasy Heel/Mud Fever involves repairing the damaged skin barrier and medicating against opportunistic secondary infections (be they bacterial, fungal or parasitic in nature).
Initially, symptomatic treatment, without a specific diagnosis is a reasonable first step in the treatment plan. Poor response to an effective, diligent, treatment plan will require a more comprehensive diagnostic approach with cytology +/- pathology.
- Provide the patient with a dry, clean environment to keep the skin of the lower limbs dry, clean and protected form further abraision.
- Do not apply anything to the skin that will further damage the skin surface. Avoid the use of chemicals (purple sprays, sulfur products, methylated spirits, bleach, sump oil etc!).
- The scabs harbour the bacteria. Soften all scabs (with warm water) and then remove. Take care to dispose of theses scabs rather than to let them contaminate the environment.
- For mild cases, apply a topical 2-3% chlorhexidine solution (not scrub) to the affected areas twice daily for a minimum of three weeks.
- If the area is ulcerated, then a topical ointment such as zinc or sudocream will be soothing and protective.
- If severe lesions are present or a poor reponse is seen to the above, then topical antibiotics will be required necessitating a veterinary consultation. Remember, most of the clinical signs associated with Greasy Heel/Mud Fever are the result of a secondary bacterial infection.
- Systemic (oral or intramuscular) antibiotics are indicated if the limb is swollen.
- Treatment is required for a minimum of three weeks.
- Pain relief is also indicated, especially if the limb/s are swollen and there is lameness evident.
- Minimise sun exposure during the acute inflamatory stage.
In summary: Treatment of Greasy Heel/Mud Fever involves avoiding further damage to the skin, repairing existing skin damage, removing scabs, medicating for a minium of 3 weeks and keeping limbs clean and dry. Antibiotics are often required. Pain relief is indicated if there is associated swelling or lameness.
References: CVE, Dermatology 2010, Proc No. 383