by Naomi Barrett
Sadly, with the buckets of rain we’ve had lashing down on us in recent weeks, many once green fields and paddocks have begun to take on an appearance closer to that of swamps and quagmires. This leaves many horses and ponies in the uncomfortable position of having to stand around in mud, which in the wrong circumstances can quickly lead to the development of the aptly named condition: mud fever. However, as you will find out, mud fever is not a problem confined to just the winter months and boggy fields alone.
How does mud fever develop?
Normal healthy skin provides a protective barrier against infectious agents. However, persistently cold and wet conditions can soften it allowing it to be easily damaged by the abrasions of grit, sand and straw. The integrity of the skin becomes compromised and bacterial and fungal organisms are able to penetrate and establish infection. The bacteria Dermatophilus congolensis and Staphylococcus species are the commonest infectious agents behind mud fever, but fungal agents such as Malassezia and Trichophyton can also be involved.
Clearly muddy conditions provide the perfect environment in which this problem can develop, which means any horse or pony could be at risk; however there are a number of other predisposing factors. Genetics have a role to play, with horses with white hair on their lower limbs and those with feathers being at greater risk. Draft horses such as Shires and Clydesdales also appear to be more prone to the condition. Previous damage to the skin by physical or chemical irritants, including contact allergies, can provide an opportunity for the infection to take hold. Equally, damage to the skin caused by unrelated infections, such as ringworm or chorioptic mange mites, can allow secondary infection to occur.
What does mud fever look like?
As a condition mud fever can vary widely in its severity. Typically it will start with small, red areas of ulceration around the back of the pastern and heels, with the back legs more commonly affected than the front. These patches of ulceration may then increase in size and scabs will form. As the disease progresses the inflamed skin exudes a smelly discharge that causes the coat to matt with the potential for complete hair loss altogether. More serious cases may see the skin of the heels split in deep horizontal fissures, an occurrence referred to as cracked heels. If infection penetrates these damaged areas the leg may become hot and swollen with cellulitis, a painful condition that can result in lameness. In the worst cases the open sores that result can really struggle to heal which may result in the formation of proud flesh, permanent hair loss and in very severe cases the need for skin grafts. Though it most often affects the lower limbs (hence its alternative names: pastern dermatitis and greasy heel), mud fever may also extend further up the legs and can even affect the belly and neck where it more often referred to as rain scald.
How to prevent mud fever?
As is often said, prevention is always better than cure. With mud fever careful management of paddocks can minimise the environmental conditions that contribute to the disease. This can be achieved by rotating horses through different fields or, if this is not possible, fencing off high traffic areas to allow them to recover. Management in an inside environment requires stables to be kept as clean and dry as possible. Using cardboard and paper as bedding is preferable as straw can be quite abrasive and shavings often stick to mud fever wounds. Washing susceptible areas can be helpful, especially with careful drying afterwards, yet care must be taken not to wash too often as this can remove naturally protective oils from the coat. Protecting susceptible areas is also worthwhile, which can be accomplished using specially designed anti-mud fever boots or with the simple use of barrier creams (such as vaseline, zinc and castor oil) so long as the area to be protected is completely dry prior to application. It is important to remember that mud fever is an infectious disease and precautions must be taken to limit the passage of infection from one horse to another. Sharing anything such as boots, wraps and grooming tools provides a potential route for cross-contamination between individuals and the infectious agents may even be carried on a rider’s hands. Stables should be thoroughly disinfected if they have housed an animal with the condition.
How to treat mud fever?
Treating mud fever lesions usually requires careful preparation of the affected area in order to be able to apply topical treatments. This is achieved by first removing the hair, either by clipping (taking extreme care not to damage the skin further) or with curved scissors. Any scabs, crusts and dirt should be cleaned away as best as possible using a gentle shampoo or a mild antiseptic wash (chlohexidine/povidine iodine are both effective at dilute concentrations) in lukewarm water. The finally preparatory step is to blot the area dry as thoroughly as possible with a clean absorbent material. Now that the leg is ready there are multiple products that can be used to treat the infection. Antibacterial shampoos containing chlorhexidine or antifungal shampoos containing miconazole, ketoconazole or enilconazole can be used on a daily basis for 7-10 days. Creams and ointments with mupirocin or a mixture of components such as neomycin, nystatin and triamcinolone are effective again the mixed infections that cause mud fever as well. Ichthammol, silver and tea tree oil based ointments are also of use and are readily available. Antiparasitics are only indicated if mites have been identified as a contributing factor or if there is a risk of flies. More severe cases where there is obvious infection or cellulitis present will require treatment with antibiotics under veterinary supervision. Non-steroidal anti-inflammatory drugs may be required to reduce the pain and swelling in such cases as well. Recovery may be aided by walking in hand on a hard dry surface, so long as lameness has been resolved, to help circulation and stimulate healing
Mud fever can be a challenging condition to treat and it may take many weeks to achieve complete healing of the lesions. In straightforward cases where the predisposing causes are readily addressed, the disease will often resolve quickly. However, in more chronic cases, the skin itself will have developed more permanent changes making it harder to treat.If you have any questions about any aspects of your horse’s health, or indeed your pet, farm or smallholding animals, please do not hesitate to contact us on 01892 835456. Putlands Veterinary Surgery is based in Paddock Wood in Kent, and offers a friendly, professional and personal service for all species of animal. We have four dedicated large animal vets with a wealth of equine experience between us, and are always happy to help.