Mud fever is frustratingly common in wet weather and treatment is not simple.

Properly called pastern dermatitis, mud fever refers to a whole range of skin reactions to a number of different irritants. It is also frequently called “greasy heels” or “cracked heels” and is caused by an infectious agent called dermatophilus congolensis, which thrives in muddy wet conditions.

The infection can stay dormant in skin, becoming active when the skin is compromised, usually by prolonged wetting. Spores germinate and produce hyphae (threadlike tentacles) that penetrate into the skin and spread in all directions from the original site. The result is an acute inflammatory reaction.

Equine skin provides an ideal medium for many bacterial organisms, as well as fungi and other parasites. These micro-organisms live on healthy skin, gaining nourishment from natural waste matter and causing no harm or active infection.

But, if the skin is injured or damaged — by a cut, wound, bite, harness sore or through prolonged wetting — the balance between host and organism is disturbed. The organism enters the horse’s body through the broken skin, and multiplies in the damp, warm epidermal layers, starting an active infection.

Causes of mud fever

Some soil types seem to predispose horses to these infections. This may explain why several animals on the same pasture become affected.

There are various other predisposing factors:

  • Prolonged damp, mild conditions
  • Standing in deep mud or soiled bedding
  • Constantly washing limbs before and/or after work without fully drying them afterwards
  • Excessive sweating under rugs or tack
  • Heavy limb feathering is frequently blamed but this is probably only because the legs tend to be washed and scrubbed more than unfeathered ones; clipping them out may not be the answer as this exposes the skin further
  • Skin trauma, such as rubbing from overreach boots or incorrectly fitted bandages, chaffing from artificial surfaces such as sand, or over-enthusiastic grooming
  • Generally unhealthy skin or the presence of a poor immune system, usually secondary to some other primary health problem
  • White limbs or patches on the body possibly due to an associated photosensitisation issue

Some horses with pastern dermatitis will be suffering from infestations of tiny chorioptic mange mites, similar to those that cause human scabies. This is most common in horses with long hair around their lower limbs, but can occur on less hairy legs. The condition is often called heel mange. Fungal infections can also be responsible for skin damage.

Another form of pastern inflammation is caused by a disorder of the body’s immune system, which attacks the skin. This is known as leucocytoclastic vasculitis and targets the unpigmented areas of the lower limbs. The condition tends to spread up the cannons. As it is usually seen on the outside and back of the limbs and sunlight is thought to aggravate it.

Signs of mud fever

The signs of mud fever are fairly classic and easy to recognise, with the distribution of the lesions reflecting the areas that have been subjected to continued wetting and trauma.

  • Matted areas of hair containing crusty scabs
  • Small, circular, ulcerated, moist lesions beneath scabs
  • Thick, creamy, white, yellow or greenish discharge (containing the causal organism) between the skin and overlying scab
  • Removed scab typically has a concave underside with the hair roots protruding
  • Deep fissures in the skin – in severe cases the skin at the back of the leg may split open, producing the horizontal fissures that are characteristic of cracked heels
  • Eventual hair loss leaving raw-looking, inflamed skin underneath
  • When found on the front legs it can be mistaken for over-reach injuries
  • Heat, swelling and pain on pressure or flexion of limb
  • Possible lameness
  • Mud fever can occur on other parts of the body, especially the back, when it is called rain scald
  • If severely affected, lethargy, depression and loss of appetite

Mud fever treatment

Keeping the skin clean and dry is the basis of treating the condition. This may only be possible if the horse is removed from the wet and mud and kept stabled for some time.

More specific treatment has to penetrate the causal organisms under the scabs, so these must be lifted and removed at the start. The horse may need to be sedated for this, as it can be very painful. Some of the tougher scabs may need soaking or poulticing first to soften them, before they can be peeled away.

Once the area is free from scabs, it should be washed — using either a mild disinfectant such as chiorhexidine, iodine wash or surgical scrub, or another a medicated shampoo — and then rinsed well.

Drying the limb thoroughly is vital — clean towels or kitchen roll can be used to blot moisture and a hairdryer is an excellent way of thoroughly drying the area if the horse will allow it.

Once dry, there are numerous creams, lotions and emollients that may help. Zinc, castor oil, lead acetate and various commercial anti-inflammatory ointments can all play a part, but only if the skin is clean and dry underneath.

Likewise, bandaging an affected limb can be a good way of keeping it clean and dry, but only if the skin has been properly prepared with beforehand, and the correct bandaging technique is used. Bandaging that’s too tight or has moisture trapped underneath can encourage an infection to flare up again.

This whole process may need to be repeated several times, and in bad cases a full recovery can take many weeks.

The use of antibiotics and anti-inflammatories will depend on the individual case and will need to be administered responsibly.

While most cases can be resolved, some chronic epidermal scarring and weakening may be left, contributing to a tendency to re-infection. Management changes to help prevent any further problems are worth pursuing.

In problem cases your vet might take a blood sample, to check liver function if the dermatitis is limited to white areas of skin only.

Make sure you know what you are treating – correct treatment from the outset can save wasted time and money. Consult your vet to obtain an accurate diagnosis and proper treatment plan.

Preventing mud fever

  • Ensure bedding is clean, dry and non-irritant at all times
  • Although many horse owners are loathed to keep their horse stabled, once the infection is established it may be the only option.
  • Avoid over-washing and/or too vigorous grooming
  • If bandaging or putting on boots, ensure limbs are clean and dry first
  • Periodically disinfect all equipment, gear and stable surfaces, as they could harbour dermatophilus spores
  • Consider topical barrier creams (usually produced in an oily base) such as tea tree oil, sulphur, MSM, aloe vera, honey with vitamin E, calendula and hypericum, goose grease and petroleum jelly. Use on clean, dry legs or underside of belly prior to turnout or exercise
  • Creams should be used with caution, as they may provide a suitable environment for bacteria to grow between the waterlogged skin and the greasy layers applied on top
  • Try using waterproof leg wraps for turnout
  • Consider nutritional supplements for promoting a healthy skin, such as soya/cod liver oils, seaweed (not for pregnant mares), antioxidants, herbs and essential oils such as lavender, camomile and yarrow
  • Rotate paddocks to avoid poaching
  • Use electric fencing to block off muddy areas around gates
  • Some horse owners find concreting or hardcoring the areas where horses congregate helps keep legs dry
  • Sand schools can irritate the skin further, as can excessive washing to remove mud and scrubbing with a stiff brush
  • Be vigilant. The sooner you spot the first telltale signs of mud fever, the quicker you can take action and so prevent a lengthy, and costly, recovery

Join H&H VIP to read tips on how to avoid mud fever from H&H’s veterinary consultant, plus a case study of a horse who got mud fever without being turned out

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