Mud Fever

This is a very common bacterial infection of the lower limbs of horses. White legs are especially susceptible and the condition is most commonly seen in the winter months particularly when the weather is wet. Wetting of the limbs seems to be an essential predisposing factor.

The infection often starts in the skin folds at the back of the pastern ('cracked heels') and spreads from there. The condition may also arise anywhere on the skin of the pastern or the cannon region. Characteristic thick painful hairy scabs develop and in some cases the lower leg may swell. Itchiness does not occur.

A related condition known as rain scald or weatherbeat affects the skin of the back and croup.

This is a complaint we often hear on our rounds. The reasons for treatment failure are likely to be some or all of these

Attempting to treat the disease without first removing all of the scabs overlying the lesions. No therapeutic agent is capable of penetrating scabby material
Using treatments which are essentially preventative (usually barrier creams of various sorts, often containing weak antiseptic agents) with minimal therapeutic effects instead of those that kill the causal bacteria (antibiotic creams and antibacterial skin washes)
Treating only part of the affected area, or more commonly stopping treatment before the condition has completely resolved
Failing to close clip the affected area. This will hugely improve the efficacy of treatment. Because horse clippers are too large and coarse to clip the hair of the heels adequately, fine (dog) clippers must be used

Anything which will soften the scabs will aid their removal. Scab removal without first softening is often difficult, and may be strongly resented by the horse. An Animalintex poultice applied for 24 hours is useful. Alternatively a generous application of baby oil, 'Dermisol' (from EqWest) or 'Sudocrem' applied to the skin, covered loosely with clingfilm and covered in turn with a stable bandage, will often have a marked softening effect after 1-3 days. It is essential that the clingfilm and bandage continue to floor level at the heels (reinforce with a few turns of duct tape) as otherwise these will ride up the pastern as it flexes leaving the lower skin crease untreated.

In some cases the clingfilm etc. treatment will have to be repeated daily for a few days until every scab can be dislodged. In spite of these softening treatments many bad cases will have to be sedated by us to allow complete removal.

Once the scabs have been softened the affected area should be washed with an antibacterial scrub such as Pevidine or Hibiscrub. The legs are wetted with warm water; the scrub is applied neat and worked in well to loosen any surface debris and scabs. The scrub is then left in place for 10 minutes (to allow a more effective bacterial kill), the legs are washed and thoroughly dried with a clean towel. This might be a good opportunity to close clip if it has not already been done.

Removing the scabs from the topline is slightly easier than from the limbs as they tend to be less tenacious. Wet the skin as before, apply neat Hibiscrub and work in well with a plastic curry comb, all the time trying to dislodge the scabs. Using one’s fingernails to remove the scabs is also effective. Leave the Hibiscrub in contact for ten minutes, then rinse and dry with a clean towel. This treatment may need to be repeated daily for several days to dislodge all of the scabs. Healing generally then occurs quickly and no further medicaments are usually necessary. The back should be kept dry until fully healed.

Removal of the scabs from the limbs will expose several 'raw' zones, usually along the skin folds at the back of the pastern. These can now be treated with an antibiotic ointment obtained from us. There are three rules about applying mud fever ointments a) there must be no scabs present, b) the raw area must first be dried by gently dabbing with a tissue to improve adherence of the ointment c) it must be applied generously.

Swelling of the leg, marked sensitivity to touch and the development of any lameness usually indicate that the infection has breached the full thickness of the skin. These cases will not respond to local treatment alone. They must have antibiotics by mouth or by injection, administered by us.

The day after

After the first treatment it is likely that some scabs will re-form overnight but these will be softer and easy to dislodge with a Hibiscrub or Pevidine wash. The raw areas as before are then dabbed with a tissue, and the antibiotic ointment re-applied. In bad cases we may recommend antiseptic washes twice daily for the first few days. Over the next few days the lesions will gradually heal but it is essential that treatment continues until the lesions have completely healed and the affected area is covered by healthy skin.

Although the condition is traditionally associated with mud coating the legs, many out-wintered horses living in muddy fields happily go through the whole winter without developing any signs. The inevitable conclusion is that it is not mud but constant wetting of the skin that is the main cause. This theory is supported by the observation that mud fever if often rife in those yards where the legs are washed frequently, and virtually absent from yards where the legs are almost never washed. It is always better to leave the mud to dry naturally on the legs (leg wraps or bandages applied over the mud will 'wick' away the moisture) and then brush off the next day.

Leg wraps are now available which the manufacturers claim keep the lower legs dry in horses at grass. It is likely however that deep mud will defeat even the best wraps.

If you must wash the legs then you must dry also. Sulphur powder or 'Keratex Mud Shield' powder sprinkled generously on the heels is very effective (even when sprinkled on wet legs) probably because these have a marked drying effect.

Although it is traditional in winter to leave the lower legs unclipped as a preventive this is probably illusory. Indeed mud fever may be more common in horses with hairier legs, due in part to the longer time these take to dry out and to the difficulty in spotting early lesions.

Waterproofing the lower limbs, the heels especially, before exercise or turn out is good practice. Thick creams such as zinc and castor oil cream, 'Sudocrem' or many of the barrier creams available from saddlers are effective. Udder cream although popular is a bit too thin for the job and hence is not very long lasting. In order to avoid getting greasy hands (and tack) every time you apply the barrier you can use a cut-down paint brush to apply it.

A New Zealand rug will help to prevent rain scald although cases do occur even with the most expensive rugs. There is a suspicion that in mild weather condensation of sweat under thick waterproof rugs may cause the condition to develop even though the rain has not penetrated

Mud fever: It is useful to get into the habit of running the fingers upwards against the direction of the hair at the back of the pastern every few days to detect the very small scabs indicating an early problem. If treated immediately these small lesions will respond very quickly.
Rain scald: In out-wintered horses the New Zealand rug should be removed at least weekly to check underneath for any early rain scald lesions, chafing by the straps etc.

If in spite of this advice you are still struggling to clear up these conditions you need to seek veterinary advice. There are a number of other conditions that may mimic mud fever and it is important that these are considered in refractory cases. In addition there is a suspicion that long term treatment with certain substances can induce a local 'allergic' response, and you may inadvertently be making the problem worse.

We have recently recognised a form of mud fever, invariably affecting the skin of the back of the pastern, which occurs during the summer and appears unrelated to wetting of the limbs. The scabs are characteristically red in colour and very tenacious. If left untreated the skin of the affected area may slough. It is unclear what is the cause of his condition. There is a suspicion that it may be related to sunlight exposure. Although treatment is similar to conventional mud fever it is often difficult and prolonged.

MUD FEVER _ GETTING IT RIGHT