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Mud fever and rain scald *H&H Plus*


  • A white check mark
    This article has been edited and approved by Karen Coumbe MRCVS, H&H’s veterinary advisor since 1991.
  • British winter weather means that when kept out, horses’ feet and hooves become waterlogged in the inevitable wet and mud, which can cause frustratingly frequent skin problems like mud fever and rain scald.

    Skin disease has been reported as a common problem in the annual Blue Cross Equine Health surveys, seen even more frequently than lameness. Sweet itch (the top summer nuisance) and mud fever (the top winter worry) accounted for nearly half (40%) of all the skin diseases recorded.

    Horse skin is amazingly delicate and when waterlogged in wet weather it becomes more susceptible to damage and infections — grooming or even being worked in a sand school can cause micro-abrasions, which let bacteria in.

    The horse’s ability to ward off infection is reduced by continuous wetting and sweating, as well as standing and being ridden in cold wet muddy conditions, hence the name ‘mud fever’. The proper name is pastern dermatitis, reflecting the range of skin reactions that affect the lower limbs due to different skin irritants, such as bacteria, fungal infections and mites.

    Mud fever [1,489 words]: Signs | Causes | Treatment | Prevention

    Mud fever is similar to a person having chapped hands or lips — the horse’s skin can become very inflamed and sore. Pink skin under white hair is more sensitive, but dark skin can be affected too. Whatever the trigger, the skin will become red, crusty and scabby and the legs will become swollen. Sometimes the hair will fall off. In severe cases the horse will be lame. Long, ‘feathered’ hair can acts as a protectant, waterproofing layer, unless it gets completely waterlogged or is infested with mites.

    Typical mud fever signs

    The signs of mud fever are fairly classic and easy to recognise, with the distribution of the sores 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 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 horizontal fissures, which is why it is sometimes called “cracked heels”. When these are found on the front legs they can be mistaken for over-reach injuries
    • Eventual hair loss leaving raw-looking, inflamed skin underneath
    • Heat, swelling and pain on pressure or flexion of limb
    • Possible lameness
    • If severely affected, lethargy, depression and loss of appetite can ensue.

    Mud fever can occur on other parts of the body, especially the back and hindquarters, when it is called rain scald, literally as a result of horses being literally being soaked to the skin repeatedly, when exposed to wet weather.

    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 because the legs tend to be washed and scrubbed more than unfeathered ones; clipping them 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 or leg 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. In persistent cases your vet might take a blood sample to check liver function, especially if the dermatitis is limited to white areas of skin only.

    Mud fever treatment

    Mud fever is a complex syndrome rather than a single disease caused by one type of bacteria — a range of skin reactions to a number of different irritants. In just the same way as there are a multitude of treatments for the common cold, there are a vast variety of mud fever remedies and careful consideration needs to be given to other underlying causes. As with any condition where there are a number of possible treatments, no one cure is effective for all cases.

    Removing the horse from the wet and mud will improve matters, although that is not always easily done. So, 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.

    It is important to know what you are treating – correct treatment from the outset can save wasted time and money, so it is recommended you consult your vet to obtain an accurate diagnosis and proper treatment plan.

    You will know if your horse’s pastern dermatitis has bacteria involved, as the skin will appear red and sore like impetigo in people. When a scab is picked off, the hair will come away with it revealing a raw area with pus beneath it. Views vary, but generally when there are scabs with infection underneath, the legs need careful cleaning and the scabs gently lifted off. Your vet may need to sedate the horse to do this effectively. Consult your vet to obtain an accurate diagnosis and proper treatment plan.

    It is wrong to assume that bacteria cause all mud fever and rain scald, which means antibiotics are not necessarily the answer. Appropriate washes can work well, but make sure they are allowed sufficient time to soak in, ideally more than 15 minutes, which is not always great in mid-winter. So use them wisely – talk to your vet to check that you are using the best antiseptic, properly and not traumatizing the skin further nor unnecessarily chilling your horse.

    Current thinking is to avoid antibiotics, or antimicrobials as they are properly called, unless they are an essential. Instead they should be saved for the worst-case scenarios. Antimicrobial resistance is an emerging clinical problem that is increasingly causing concern amongst vets and doctors. So think carefully before considering antimicrobials for the horse with scabby skin, as it is unlikely to produce a permanent cure and it may not help at all. If there is a management improvement that you can make, try that first.

    Usually chlorhexidine is recommended to wash the limbs. 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 thoroughly if the horse will accept 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, otherwise any infection may be exacerbated under the layer of grease.

    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. Some horses may be really quite sore, so your vet may prescribe anti-inflammatories, but this will depend on the individual case and your vet’s advice.

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

    Preventing mud fever

    It is important to 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. There are also basic steps that can help avoid it in the first place.

    • Ensure bedding is clean, dry and non-irritant at all times
    • Although many horse owners are reluctant to keep their horse stabled, once the infection is established it may be the only option
    • Avoid over-washing and/or extremely vigorous grooming
    • If bandaging or putting on boots, ensure both limbs and boots/bandages are clean and dry
    • 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. Only use on clean, dry legs 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 water resistant leg wraps for turnout, provided they do not rub delicate skin.
    • Consider nutritional supplements for promoting a healthy skin and also ensure the skin is not damaged by close clipping.
    • Rotate paddocks to avoid poaching
    • Use electric fencing to block off muddy areas around gates
    • Some horse owners find concreting or putting down hardcore in the areas where horses congregate helps keep legs dry

    Whatever you do to prevent this, mud fever remains a very common condition of horses turned out in British winter weather.