Mud fever is a skin condition affecting the lower legs of horses, most commonly the heels and pasterns. It develops when prolonged exposure to wet, muddy conditions damages the skin’s natural barrier, allowing bacteria, fungi, or other organisms to invade and cause infection. Known in veterinary medicine as pastern dermatitis (and sometimes called “scratches” or “greasy heel”), it ranges from mild scabbing to painful, swollen legs that can make a horse lame.
What Causes Mud Fever
The name suggests mud is the culprit, but it’s really moisture. Standing in wet, muddy fields softens the skin on a horse’s lower legs, creating tiny cracks and breaks. Those breaks become entry points for bacteria and fungi that live naturally in soil. The bacterium most consistently linked to mud fever belongs to the Staphylococcaceae family, though a mix of organisms is usually involved. Dermatophilus congolensis, a bacterium that thrives in wet conditions, is another well-known cause. Fungal organisms, parasitic mites, and even prolonged contact with urine-soaked bedding can trigger the same type of skin breakdown.
Mechanical injury to the skin also plays a role. Anything that disrupts the skin barrier, including grit in sand arenas, rough footing, or even sweat trapped under boots and bandages, can set the stage for infection. Stress, concurrent illness, and tick infestation can weaken a horse’s immune response and make them more vulnerable.
Which Horses Are Most at Risk
Mud fever can affect any horse, but some are significantly more prone. Horses with white markings on their lower legs have unpigmented (pink) skin beneath, which is thinner and less able to absorb UV light or resist environmental damage. Studies across multiple breeds have confirmed that legs with white markings up to pastern level develop pastern dermatitis more frequently than pigmented legs, particularly in lighter breeds like Warmbloods. Hind legs are also affected more often than front legs across breeds.
Heavy breeds with thick feathering around the fetlocks face a different challenge. Dense leg hair traps moisture against the skin for hours, creating the perfect warm, damp environment for bacteria to multiply. Feathering also hides early signs, so by the time an owner notices something is wrong, the infection may already be advanced. Horses kept on poorly drained land, turned out in persistent rain, or standing in deep mud around gateways and water troughs are at the highest risk regardless of breed.
How to Recognize It
The earliest sign is usually matted hair or small crusty scabs on the back of the pastern or heel. At this stage, the skin underneath may look pink, irritated, or slightly swollen. As the condition progresses, you’ll notice:
- Crusty scabs forming on the heels or lower legs, sometimes extending up toward the fetlock
- Hair loss in patches, with raw, reddened skin underneath
- Discharge between the skin and scabs, ranging from creamy white to yellow or green
- Heat and swelling in the lower limb, with the horse reacting to touch
- Lameness in severe cases, particularly when infection spreads deeper into the tissue
Mud fever can be genuinely painful. Some horses won’t tolerate having the area handled at all, which makes treatment tricky. Infections developing beneath the scabs can worsen quickly, and significant leg swelling signals that the infection may be spreading beyond the skin surface into the underlying soft tissue.
Cleaning and Treating Affected Legs
Successful treatment starts with removing the bacteria’s hiding spots: the scabs. This is often the hardest part, because the scabs are painful to remove and horses understandably resist. The recommended approach is to wash the affected area with a very dilute antiseptic solution (a 0.1% dilution is standard). Lather it on and leave it for about 10 minutes to soften the crusts before rinsing thoroughly with warm, clean water. Never use cold water, and never apply undiluted antiseptic directly to the skin.
After washing, dry the area completely. This step matters as much as the cleaning itself, since leaving the skin damp will only perpetuate the problem. In horses with thick feathering, you may need to clip the hair away entirely to allow thorough cleaning and proper drying. Once the area is clean and dry, leaving it exposed to air overnight helps the skin begin to heal.
For mild cases, topical antibacterial ointments applied to the cleaned skin can control the infection. Your vet may also prescribe a topical steroid cream to reduce inflammation and pain. If the horse lives out full-time and you can’t bandage the legs, the routine shifts to regular washing and thorough drying as often as needed to keep the area clean. Consistency matters more than any single product.
When It Needs Veterinary Attention
Most mild cases respond well to diligent home care over one to two weeks. But severe lameness, deep wounds, significant swelling, excessive heat, or thick yellow or green discharge are signs the infection has progressed beyond what topical treatment can handle. At that point, systemic antibiotics may be necessary. A vet can also take skin samples for bacterial and fungal cultures, which is particularly useful for cases that keep coming back or don’t respond to standard treatment. Biopsy may be recommended in chronic cases to rule out other underlying conditions like photosensitivity reactions, mite infestations, or allergic responses that can look very similar to straightforward mud fever.
Preventing Mud Fever
Prevention centers on one principle: keep the lower legs as dry as possible. This sounds simple, but in a British or northern European winter, it’s a genuine management challenge. A few strategies make a real difference.
Check your horse’s legs daily, running a hand over the heels and pasterns to feel for scabs, heat, or sensitivity before they become visible. Catching mud fever early, when it’s just a small patch of rough skin, is far easier to treat than waiting until the entire pastern is crusted and swollen.
Applying a thick barrier cream to clean, dry legs before turnout creates a water-resistant layer between the skin and the mud. These creams should only go on healthy skin, never over existing sores or scabs, which would trap infection underneath. Mud fever boots and turnout “socks” are another option that physically shield the lower legs from wet conditions.
Field management helps too. Minimizing poaching (the churning of ground into deep mud) around gateways, shelters, and water troughs reduces exposure. Hard standing or rubber matting in high-traffic areas gives horses somewhere dry to stand. Rotating fields, improving drainage, and avoiding overcrowding all reduce the amount of time legs spend submerged in mud. For horses that are particularly susceptible, limiting turnout during the wettest periods or choosing drier, better-drained paddocks can prevent repeated bouts entirely.