Mud Fever in Horses: Causes, Treatment, and Prevention

Every winter it happens. The fields turn to soup, the horses stand in it for hours, and then someone walks into the barn and notices their horse flinching when you try to pick up a hind foot. You look closer. The skin on the back of the pasterns is angry, red, cracked, and weeping. Scabs are forming. The hair is matting into crusty clumps. Congratulations, you've got mud fever.

Also called scratches, greasy heel, or pastern dermatitis (the proper clinical name), mud fever is one of the most common skin conditions in horses kept in wet environments. It ranges from mildly annoying to genuinely debilitating, and the horses that get it worst are often the ones whose owners didn't catch it early enough or treated it incorrectly. It's not glamorous veterinary medicine. Nobody writes dramatic novels about pastern dermatitis. But if your horse can barely walk because the skin behind their fetlocks has cracked open and become infected, it becomes the only thing that matters.

What's Actually Causing This

The primary culprit is Dermatophilus congolensis, a gram-positive actinomycete bacterium that's honestly fascinating if you're into microbiology (and maddening if you're trying to get rid of it). D. congolensis exists in the environment and on the skin of many horses without causing problems. It produces zoospores that sit dormant until conditions are right. What activates them? Moisture. Prolonged, persistent moisture.

Healthy skin is a remarkably effective barrier. The epidermis has a lipid layer, a physical structure of keratinized cells, and a population of normal commensal bacteria that outcompete pathogens. When skin stays wet for extended periods, that barrier softens. The keratin layer macerates. Tiny cracks and fissures develop. Commensal bacteria get flushed away. And suddenly Dermatophilus zoospores have a front door to walk through.

Once the bacteria penetrate the epidermis, they form branching filaments that spread laterally through the superficial skin layers. The immune response generates an inflammatory exudate that mixes with damaged keratinocytes to form the characteristic thick, crusty scabs. Beneath those scabs, the skin is raw, painful, and oozing. Pull off a scab and you'll often see the underside has a concave, pitted appearance with a tuft of hair embedded in it. That's classic Dermatophilus.

But here's the thing. Mud fever isn't always just Dermatophilus. Secondary invaders love compromised skin. Staphylococcus species, Pseudomonas, and sometimes fungal organisms (particularly Dermatophytes) can pile on. In chronic cases, you might be dealing with a polymicrobial infection that's far harder to clear than a straightforward bacterial issue. Photosensitization can contribute too, especially on white or unpigmented skin of the pastern, where UV-activated compounds in certain plants cause dermatitis that looks and behaves like mud fever.

Who Gets It and Why

Any horse can develop mud fever given enough mud and moisture. But some are dramatically more susceptible than others.

Heavy-feathered breeds top the list. Shires, Clydesdales, Friesians, Gypsy Vanners, and their crosses. All that luxurious feathering traps moisture against the skin of the pastern and heel. It creates a warm, damp microenvironment that Dermatophilus absolutely loves. The feathering also makes early detection harder because you can't see the skin without lifting and parting the hair. By the time you notice the horse is sore, the infection may be well established.

Horses with white legs (unpigmented skin) are more vulnerable. Pink skin has less melanin, which means less UV protection and potentially a thinner, more reactive epidermis. Many experienced horse people will tell you their chestnut with four white socks gets scratches every winter while the bay in the next field stays clean. This is a real observation backed by dermatological principles, not just barn lore.

Management factors matter enormously. Standing in muddy paddocks for hours. Legs that get hosed off and never properly dried. Turnout boots that trap moisture. Sand or gravel footing that abrades the skin. Dirty bedding in stalls. All of these compromise the skin barrier and invite trouble. Some operations run their horses through a wash rack daily and wonder why the pasterns are falling apart. The washing itself can be part of the problem if the skin never fully dries.

Immune status plays a role in severe or recurrent cases. Horses with Cushing's disease (PPID) are notoriously prone to skin infections, including mud fever, because their immune surveillance is impaired. If you've got a horse over 15 that gets mud fever every year despite good management, it might be worth testing ACTH levels.

What It Looks Like: Stages of Progression

Mild mud fever starts with reddening and slight swelling of the skin on the back of the pasterns. The hair might look ruffled or dull in the area. You might notice the horse is slightly sensitive when you brush or touch the heels. At this stage, catching it and responding quickly usually means a fast resolution.

Moderate cases progress to visible scabbing, crusting, and matting of hair. The skin beneath the scabs is raw, pink to red, and may be weeping serum or pus. The horse resists having the area touched. There's often mild swelling of the pastern. You might notice the horse standing with the affected foot slightly forward, trying to reduce pressure on the heel.

Severe mud fever is genuinely ugly. The entire pastern and sometimes the cannon bone are swollen, hot, and painful. Scabs are thick, extensive, and layered. The skin between scabs is cracked and oozing. In the worst cases, cellulitis develops: bacterial infection spreads into the deeper subcutaneous tissue, causing dramatic limb swelling ("stocking up" that won't resolve with exercise), heat, pain, and systemic signs like fever and depression. Severe cellulitis from pastern dermatitis can cause permanent thickening of the limb if not treated aggressively. Chronic progressive lymphedema in draft breeds represents the extreme end of this spectrum. For a broader look at equine skin issues, see our overview of common horse skin conditions.

Treatment: Getting It Under Control

The fundamental principles are simple: clean, debride, treat, protect, dry. Executing them on a painful horse that doesn't want you anywhere near its heels is the hard part.

Step 1: Soften and Remove Scabs

Those scabs harbor bacteria underneath them. Topical treatments can't reach the infection while the scabs are in place. But ripping scabs off a painful horse is cruel and counterproductive because it damages the healing tissue beneath. Instead, soften them. Apply a thick layer of an emollient like petroleum jelly, coconut oil, or a commercial barrier cream and leave it on for 12-24 hours. This loosens the scabs so they can be gently peeled or washed away without causing fresh trauma. Some people use warm, dilute chlorhexidine (0.5-1%) or betadine (diluted to tea-color) soaks instead. Both work.

Step 2: Wash Carefully

Once scabs are softened, gently wash the affected area with an antimicrobial shampoo. Chlorhexidine-based shampoos (2-4%) are the most commonly recommended. Benzoyl peroxide shampoo (2.5-3%) is excellent for flushing follicles and cutting through greasy exudate. Leave the shampoo on as a contact treatment for 10 minutes before rinsing. This matters. A quick lather-and-rinse doesn't give the antimicrobial enough contact time to work.

Step 3: Dry Thoroughly

This step gets skipped too often and it's arguably the most important one. After washing, dry the area completely. Towel dry first, then let it air dry in a clean environment, or use a low-heat blow dryer if the horse tolerates it. Applying topical treatments to damp skin traps moisture against the damaged epidermis and feeds the very organisms you're trying to kill. Dry, dry, dry.

Step 4: Topical Treatment

Options abound. Silver sulfadiazine cream (Silvadene) is a veterinary and human medicine staple for infected skin wounds. It's effective against Dermatophilus and most secondary bacteria. Apply a thin layer to the affected area once or twice daily. Mupirocin ointment works well for Staph-heavy infections. Flamazine (another silver sulfadiazine formulation) is popular in the UK and Europe.

Over-the-counter options include zinc oxide-based barrier creams (Desitin, Sudocrem) applied after antimicrobial treatment to protect the healing skin and repel moisture. Some horsepersons swear by a 50/50 mix of Desitin and antifungal athlete's foot cream. It sounds ridiculous but actually addresses both bacterial and fungal components while providing barrier protection.

Step 5: Systemic Treatment for Severe Cases

When cellulitis is present, or when the infection covers a large area and isn't responding to topical treatment alone, systemic antibiotics are warranted. Trimethoprim-sulfonamide (TMS) is commonly prescribed as a first-line oral antibiotic. It's effective against Dermatophilus and most common secondary bacteria, it's affordable, and it's available in oral paste or powder form. More severe cases may require potassium penicillin or procaine penicillin injections. Your vet may also prescribe a short course of anti-inflammatories (phenylbutazone or flunixin) to manage pain and swelling, especially if the horse is significantly lame.

The Feathered Breed Challenge

Managing mud fever in Shires, Clydesdales, and similar breeds deserves its own discussion because it's a fundamentally different challenge. The feathering creates a microclimate around the pastern that's nearly impossible to keep dry during wet seasons. And clipping the feathering, while it solves the moisture problem, is aesthetically devastating to owners who chose these breeds partly for their feather.

Some draft breed enthusiasts clip the pasterns in winter and allow regrowth for show season. This is probably the most practical approach. Others manage by applying barrier products (like pig oil mixed with sulfur powder, a traditional British remedy) to the feathering and skin before turnout. The oil repels water while the sulfur discourages bacterial growth. It works, but it needs reapplying every few days and it makes the feathering look greasy.

Chronic progressive lymphedema (CPL) in draft breeds is a related but distinct condition involving impaired lymphatic drainage that leads to progressive swelling, fibrosis, and skin folding in the lower limbs. CPL predisposes to secondary bacterial infection that looks like mud fever but doesn't respond to conventional treatment because the underlying lymphatic dysfunction persists. There's no cure for CPL, only management. If your draft horse gets recurrent "mud fever" that never fully resolves despite aggressive treatment, CPL should be investigated. More on this at pastern dermatitis conditions.

Prevention: Worth Ten Times the Cure

Reduce mud. Obvious, right? But it's the single most impactful thing you can do. Gravel pads around gates, water troughs, and feeding areas where horses congregate. Sacrifice paddocks with footing material rather than bare earth during the wet months. Rotational grazing to prevent pasture destruction. French drains in chronically waterlogged areas. These infrastructure investments pay for themselves in reduced vet bills and horse suffering.

Barrier products before turnout on vulnerable horses work well. Petroleum jelly, zinc-based creams, or commercial products like Keratex Mud Shield Powder create a physical barrier between wet mud and skin. Apply to clean, dry skin before turnout. It's an extra five minutes of work that can prevent weeks of treatment.

Dry legs properly when they come in wet. If you wash mud off legs (and sometimes you have to), follow up with thorough drying. Some barns keep microfiber towels specifically for this purpose. They absorb water far better than terrycloth and are easier to launder.

Check legs daily during high-risk seasons. Run your fingers down the back of the pasterns. Feel for heat, sensitivity, crusty spots, or matted hair. Five seconds per leg. Catching mud fever on day one means a topical cream and some dry time. Catching it on day fourteen means a vet visit, systemic antibiotics, and a horse that doesn't want anyone near its legs for a month. Explore our anatomy resources to understand the structures underneath the skin that can be affected when infection spreads deep.

Frequently Asked Questions

Sources

• Scott, D.W. & Miller, W.H. (2011). Equine Dermatology, 2nd ed. Elsevier Saunders.
• Merck Veterinary Manual: Dermatophilosis in Animals. merckvetmanual.com.
• Pilsworth, R.C. & Knottenbelt, D.C. (2007). Pastern dermatitis. Equine Veterinary Education, 19(10), 529-530.
• De Cock, H.E.V. et al. (2003). Chronic progressive lymphedema in draft horses. Veterinary Pathology, 40(1), 97-101.
• American Association of Equine Practitioners (AAEP). Skin Diseases in Horses. aaep.org.
• Royal (Dick) School of Veterinary Studies, University of Edinburgh. Equine Dermatophilosis factsheet.