Mud fever is the term given to a painful inflammatory condition involving the skin of the lower limbs, although it can extend above the pasterns. It is one of a collection of diseases collectively referred to as pastern dermatitis. It is characterised by swelling, redness of the skin, pain, which can be severe, in addition to scabbing and crusting of the skin. It’s more commonly found in white limbs, and in heavily feathered breeds. 

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What causes mud fever?

Causes of pastern dermatitis include, but are not limited to, bacterial infection, fungal infection, infestation with leg mites (Chorioptes) or harvest mites (Neotrombicula autumnalis), photosensitisation or autoimmune disease. In general, when we refer to mud fever, we are referring to the infection of the lower limbs with the bacteria Dermatophilus congolensis. Usually this gains entry to the skin through abrasions caused by trauma or by inflammation due to chronic wetting of the skin. 

How is it diagnosed?

As previously mentioned, the clinical signs include pain and swelling of the lower limbs, with one or more legs affected. Scabs are usually present as the disease becomes established. These scabs tend to come off with clumps of hair and can be associated with yellow oozing or crusting. Lameness can be mild to very severe and it can develop very quickly. 

In many cases, your vet may diagnose and subsequently treat mud fever based on the clinical signs and history alone and resort to further testing in unusual or refractory cases. In these cases, your vet will be able to carry out some tests; such as culture or examination of swabs for bacteria or fungi, skin scrapes, biopsy or blood samples to determine the exact cause or the presence of any underlying pathologies. One example of an underlying condition is equine leukocytoclastic vasculitis, best diagnosed by biopsy.

How is it treated?

It can be difficult to catch mud fever early. But careful investigation of your horse’s legs at least once a day will help to spot any signs. It can be difficult to perform a thorough check in the dark, damp winter nights. But early diagnosis and prompt treatment will greatly improve success rates. 

In the first instance, consult your vet who will confirm the diagnosis. They will be able to advise and start treatment as necessary. 

Changing the environment is the first and most important step

It is imperative that affected legs are kept clean and dry in order to treat the condition. This can be extremely challenging when stabling or hard standing is not available. 

Clipping away feathers and thick hair coat will help to allow the skin and lesions to dry

Remember, skin cannot heal easily while damp, contaminated hair is present. Many of these cases are extremely painful, which can make clipping an agonising and potentially dangerous task. In these situations, it may be necessary for your vet to attend to provide appropriate analgesia and sedation if necessary. In some cases, it may be necessary to start treatment with an aim to make the horse comfortable enough to tolerate clipping.

If you do clip your horse, remember that the clippers will become contaminated with bacteria from the scabs. Please ensure that you disinfect them between horses.  

One of the main aims of treatment is to remove the scabs from the skin

As previously mentioned, scab removal can be extremely painful for the horse. In these cases, covering the legs with an antimicrobial thick oil-based cream and allowing this to soak in will help to remove the offending scabs. It is very helpful to cover the legs with cling film under a layer of stable bandage to allow the cream to penetrate overnight. Once the cream has been given adequate time to penetrate and loosen the scabs, they can be removed more easily by wiping the skin with a clean disposable cloth. It is important to dispose of this cloth after every use as it will be heavily contaminated with bacteria. 

It is also advisable to disinfect the surrounding area once the treatment is completed; this is to avoid re contamination of the legs. It is advisable to treat the horse on an area of hard standing; rather than in a stable where bedding could become contaminated. Any equipment and surface should be disinfected after each treatment.

Shampooing the legs with dilute shampoo in warm water will help 

It acts to reduce the scaling and crusting and so reduce the bacterial load on the skin, and will also allow further penetration of antimicrobial cream. Dilute chlorhexidine is often used for this, but this can be quite drying on the skin. Commercially available shampoos containing colloidal oatmeal may result in better preservation of the skin. 

Your horse may need pain relief 

This is usually in the form of anti-inflammatories, such as phenylbutazone which can be prescribed by your vet. Occasionally cases may benefit from antibiotics, but not all cases will be given antibiotics in the first instance. This decision will be made by your vet after a clinical examination. Some horses may benefit from topical steroid cream once the bacterial infection has resolved. 

In conclusion, the main aim of treatment is to remove contaminated scabs and to keep the skin clean and dry 

Any underlying conditions such as mite infestation will also need to be treated. One recent small study found that topical treatment with essential fatty acids helped to reduce the severity, but not prevent, mud fever in a small select group of cases. This may form the basis for future research and development. 

Can it be prevented?

Ideally horses would be kept in clean and dry conditions to prevent this. However, this is often not possible, particularly during long spells of wet conditions and where grazing is limited leading to poaching of fields and gateways. 

If you do have to turn your horse out in muddy conditions, rinsing the mud off may help. But care should be taken to dry the legs thoroughly. Use a clean towel that can be washed between uses to reduce re-infection. Some people will even use a hair dryer for this, if the horse will tolerate it.

It may be advisable in healthy horses, to let the mud dry onto the feathers or hair before brushing it off; as this avoids chronic wetting of the skin, which may increase the risk of mud fever developing. Some horse’s skin is particularly sensitive to repeated wetting, so in these animals, letting the mud dry is preferable. 

Commercially available dry boots can be helpful in some cases. But care must be taken to ensure that they are fitted properly as if not, any loose dirt or grit will rub the legs. This can lead to abrasions which will allow bacterial infection to develop. 

To clip or not to clip? 

The feathers are evolved to protect a horse’s legs. But if they are constantly wet and mud laden, they may exacerbate the problem. As a general rule, if the skin on the legs is intact, then the feathers may be useful in preventing disease. However, if mud fever has set in, clipping may help with treatment as it will improve the chances of keeping the skin dry.

Barrier creams can be helpful in some individual cases

However, they can create a moist environment in which bacteria can thrive. If you choose to use these, they should only be applied to clean, dry skin. And the cream should be removed regularly to ensure that the skin beneath remains healthy. 

It can be difficult to catch mud fever early, but careful investigation of your horse’s legs at least once a day will help to spot signs of early disease

It can be difficult to perform a thorough check in the dark, damp winter nights, but having even a small area of hard standing will help with this. If your horse does develop mud fever, intensive treatment and management may be needed and for this, stabling or hard standing is extremely useful. If your horse is not responding to treatment, your vet may decide to carry out further investigation to check for underlying conditions. 

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