Mud Fever in Horses: Causes, Treatment and Prevention

Reviewed by Dr. Ali Ehtisham, DVM

As autumn arrives and fields become waterlogged, equine yards across the country prepare for one of the most common and persistently frustrating problems in horse management: mud fever. Also known as pastern dermatitis or, when it appears on the body, rain rot, mud fever is a bacterial skin infection of the lower leg that affects thousands of horses every winter. It is painful for the horse, time-consuming for the owner, and deceptively tricky to resolve if the treatment principles are not followed correctly. This guide covers everything from the biology of the condition to the practical management steps that make the difference between a case that clears up in a fortnight and one that drags on for the entire winter.

What Is Mud Fever?

Mud fever — its formal veterinary name is pastern dermatitis — is a bacterial infection of the skin below the fetlock, most commonly caused by Dermatophilus congolensis. This organism is classified as an actinomycete — a type of bacterium with some filamentous growth characteristics — and it is found naturally in the environment and on the surface of healthy skin in many horses. Under normal circumstances, it causes no harm. The infection only becomes established when the skin barrier is compromised, allowing the organism to penetrate the outer layers and create an active infection in the dermis and epidermis.

The same organism, Dermatophilus congolensis, causes rain rot (or rain scald) when it affects the back, neck, and quarters — typically following prolonged wet weather that saturates a horse's coat and skin over large areas. The clinical appearance differs because the body surface affected differs, but the underlying biology is identical. Both conditions represent opportunistic infection of skin that has been weakened by prolonged moisture exposure.

In some mud fever cases there is also a fungal component — fungi such as Fusarium species can contribute to the infection, particularly in chronic or resistant cases. This has practical treatment implications: purely antibacterial topical products may not be effective against a case with a significant fungal element, and combined antibacterial-antifungal treatments or products with broader-spectrum activity may be needed.

How Wet Conditions Break Down the Skin Barrier

Normal equine skin is an effective physical and biochemical barrier against environmental microorganisms. The outer layers of the epidermis — the stratum corneum — provide a tough, relatively waterproof surface. Sebum produced by sebaceous glands provides a mildly antimicrobial, water-resistant film over the skin surface. The skin's resident microbiome competes with potential pathogens for the available niche. Together, these defences prevent the vast majority of environmental organisms — including Dermatophilus — from establishing infection.

Prolonged wet conditions undermine all of these defences. Water-logging of the skin softens and swells the stratum corneum, reducing its mechanical resilience. Repeated wetting and drying cycles — the pattern typical of a horse that is turned out in muddy fields and then stabled — are particularly damaging, creating micro-cracks in the skin surface. Abrasion from mud particles acts like sandpaper on already-compromised skin. Minor cuts, insect bites, and dermal grazes provide direct entry points. Once the barrier is broken, Dermatophilus and other organisms gain access to the moist, warm environment of the dermis that they need to proliferate.

Which Horses Are Most at Risk?

Horses with white legs are significantly more susceptible to mud fever than those with pigmented legs. This is not folklore — it is a well-documented clinical observation with a plausible biological explanation. Skin pigmentation by melanin affects the structural properties of the epidermis: melanin granules within keratinocytes appear to contribute to the physical resilience of the skin barrier, and skin with reduced melanin is more permeable and less resistant to environmental challenge. Horses with four white legs below the knee and hock are substantially more susceptible than horses with fully pigmented legs. Owners of horses with white legs need to be especially vigilant about mud fever prevention in wet conditions.

Heavily feathered breeds — Clydesdales, Shires, Friesians, Gypsy Cobs, and other heavy horses — are at elevated risk for a different reason. The thick, heavy feathering that covers the lower legs of these breeds creates a warm, humid microenvironment at the skin surface that remains wet for extended periods after rain or field turnout. The feathering prevents air circulation and traps moisture against the skin, reproducing the conditions that enable Dermatophilus infection even in horses that spend relatively little time in wet fields. These horses also carry a higher risk of chorioptic mange (skin mites under the feathering) that can compound and complicate mud fever management.

Any horse subjected to prolonged wet conditions is at risk regardless of leg colour or coat type. Management is the primary determinant of risk for most horses.

Recognising Mud Fever: Signs to Look For

Mud fever typically develops in the skin below the fetlock, most commonly on the back of the pastern and fetlock — areas that are in constant contact with wet ground and experience the most repetitive wetting and drying. In more severe cases it extends upwards onto the cannon bone, and in very severe cases can involve the entire lower leg.

The characteristic early sign is the formation of crusty scabs — raised, firmly adherent scabs with matted hair trapped in them. Removing a scab reveals moist, inflamed, often bleeding skin beneath. The underlying skin is typically pink to red and painful on palpation. In active infection, the scabs are full of bacterial colonies — the characteristic "paint brush" appearance of bacteria growing between the skin and the overlying scab is visible on microscopy.

As the condition progresses, additional signs emerge: swelling of the lower leg, heat, sensitivity when the leg is handled, and lameness in more severe cases. The horse may show reluctance to bear weight on the affected leg, particularly if swelling has progressed into the deeper tissues. In cases where infection has spread upward into the subcutaneous tissue — cellulitis — the swelling becomes more pronounced, often extending well above the fetlock, and the leg feels tight and hot. Cellulitis is significantly more serious than surface mud fever and requires prompt veterinary intervention.

Treatment: The Critical First Step

The single most important — and most commonly skipped — step in treating mud fever is removing all of the scabs. This cannot be emphasised strongly enough. The scabs provide physical protection to the bacteria underneath them, and any topical antibacterial product applied over intact scabs is prevented from reaching the organisms causing the infection. Treatment that leaves scabs in place does not work.

Scab removal is most effectively and least painfully achieved by first softening the scabs. Soaking the leg in warm water with added chlorhexidine scrub (a standard antibacterial product used in equine wound care) for 10–15 minutes softens the scabs significantly, reducing the discomfort of removal. A gentle but firm approach to scab removal — using the fingers or a soft cloth — should remove the scabs completely, exposing the inflamed skin beneath.

After scab removal, the leg should be gently cleaned of any remaining debris, rinsed, and then — critically — dried thoroughly. Drying is the step that many owners underemphasise, yet it is fundamental to treatment success. Wet skin does not heal. If the leg is cleaned but not dried before applying topical treatment, the treatment is applied over a still-compromised skin barrier. In cold weather, a stable bandage or leg wrap applied over the dry leg helps maintain warmth while the skin dries and begins to heal.

Following scab removal and drying, an appropriate topical treatment should be applied. Your veterinarian will recommend a specific product based on the severity and nature of the infection — options include antibacterial creams (containing fusidic acid, silver sulfadiazine, or other antibacterial agents), combined antibacterial-antifungal preparations, and barrier products that both treat the infection and protect the healing skin from further moisture exposure. Do not apply over-the-counter wound treatments or petroleum jelly to active infection — barrier products alone are appropriate for prevention, not treatment of established infection.

Keeping the legs dry between treatments is essential and is often the most logistically challenging part of management. A horse that is turned out in wet fields each day while being treated for mud fever is being treated and re-exposed to the precipitating cause simultaneously. In mild cases this can still resolve with diligent treatment; in more severe cases, dry conditions during treatment are necessary for recovery. Options include box rest, use of a dry sacrifice area, or limiting turnout to dry periods.

Cases that are severe, painful, involve significant swelling, are not responding to topical treatment after one to two weeks, or in which lameness is present require veterinary attention. Systemic antibiotics (given by injection or orally) are needed when infection has penetrated the deeper tissues or when a surface infection is too extensive or well-established to be managed topically alone.

Mud Fever Under Feathering

Managing mud fever in heavily feathered horses presents particular challenges. The feathering prevents the legs from drying naturally and makes inspection of the skin beneath difficult. Many owners do not discover mud fever in feathered horses until the infection is well established, because the scabs and skin changes are hidden under the coat.

Clipping the feathering is the most effective approach to managing mud fever in these breeds — it allows the skin to be properly inspected, cleaned, dried, and treated, and removes the moisture-trapping environment that enabled the infection in the first place. Many Friesian, Clydesdale, and cob owners are reluctant to clip feathering, but in a horse with active mud fever, maintaining the feathering makes effective treatment very difficult.

For prevention in feathered horses, daily inspection and drying of the lower legs after wet conditions, the use of barrier products before turnout, and regular checking for early skin changes is the minimum standard. Some owners use waterproof leg wraps or boots to protect the lower legs during turnout in wet conditions, which can reduce the frequency of mud fever episodes in susceptible individuals.

Prevention

Prevention of mud fever involves reducing the duration and severity of wet skin exposure on the lower legs. No single measure eliminates risk entirely, but a combination of the following approaches significantly reduces incidence.

Field management is the foundation. Fields with standing water, deep mud, and poor drainage are direct contributors to mud fever risk. Restricting access to the worst areas using electric fencing, providing a well-drained gateway area with hard standing or rubber matting, and rotating fields to prevent overuse during wet periods all reduce the amount of time the lower legs spend in wet mud.

Barrier creams — petroleum jelly-based products or proprietary equine barrier preparations — applied to clean, dry legs before turnout provide a physical barrier between the skin and wet ground. They work best as a preventive measure in horses at risk; they are not a treatment for active mud fever.

Cleaning and drying after wet conditions — establishing a routine of washing the legs, removing mud and debris, and then drying the legs thoroughly before stabling reduces the cumulative skin exposure that predisposes horses to mud fever. Some owners prefer not to wash legs after every turnout, allowing mud to dry and brushing it off — this approach avoids the repeated wetting that washing can introduce if drying is not thorough.

Regular inspection — particularly in high-risk periods — allows early detection and prompt treatment of minor skin changes before they become established infections.

When to Call the Vet

Contact your veterinarian if: the horse is lame on the affected leg; significant swelling extends above the fetlock; the leg is acutely hot, swollen, and painful in a pattern suggesting cellulitis; the condition is not improving after one to two weeks of correct treatment; or you are unable to remove scabs because the horse is too painful to tolerate the procedure. Severe cases of cellulitis are genuine veterinary emergencies — the infection can spread rapidly and cause lasting damage to the lymphatics of the lower leg.

Frequently Asked Questions

What causes mud fever in horses?

Mud fever is caused by Dermatophilus congolensis — an opportunistic bacterium that penetrates skin softened and compromised by prolonged wet conditions. White-legged horses are more susceptible; heavily feathered breeds are at elevated risk because feathering traps moisture against the skin.

Should I remove mud fever scabs?

Yes — this is the most critical treatment step and the most commonly skipped. Scabs protect the bacteria from topical treatment; treatment applied over intact scabs cannot reach the infection. Soak in warm chlorhexidine solution for 10–15 minutes, then remove all scabs before applying any treatment.

How long does mud fever take to heal?

Mild cases caught early and treated correctly typically resolve in one to three weeks. More established cases or those with a fungal component take longer. Cases that have progressed to cellulitis require veterinary treatment and may take several weeks. The key variable is the ability to keep the legs clean and dry during treatment.

Can mud fever spread up the leg?

Yes — in severe or neglected cases the infection can spread upward, and if it penetrates into deeper tissues it becomes cellulitis, causing significant swelling, heat, pain, and lameness. Cellulitis requires prompt veterinary treatment including systemic antibiotics. Lameness or swelling above the coronary band warrants immediate veterinary contact.

How do I prevent mud fever?

Improve field drainage, apply barrier cream to clean dry legs before turnout, keep legs clean and thoroughly dry after wet conditions, restrict access to the muddiest areas, and inspect lower legs regularly. Early treatment of minor skin changes prevents progression to established mud fever.

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Disclaimer: This article is for educational purposes only and does not constitute veterinary advice. Always consult a licensed equine veterinarian for diagnosis and treatment.