Mud fever (greasy heel) and rain scald, also known as dermatophilosis are all too common in horses in New Zealand. Both are skin infections caused by the bacterium Dermatophilus congolensis. This bacterium is a normal inhabitant of the skin of horses but it can cause infections when there is persistent wetting or damage to the skin.

Mud fever affects the lower limbs.

  • There are crusts, scabs, and cracks in the skin.
  • The lower legs (where all the rain and sweat gravitate) are the sites most often affected.
  • Sometimes there is swelling particularly of the pastern, and the horse may be lame.
  • Non-pigmented skin (white socks) is susceptible to mud fever because it lacks the pigment that helps to protect against the damaging effect of the sun.

Rain scald lesions are distributed over the body, neck, and head.

  • In typical cases, there is a rash of small scabs over the skin surface.
  • It’s common under covers that are not waterproof so that the skin underneath is persistently damp.
  • The crusts or scabs stick to clumps of hair so that the matted hairs come with them when the scabs are removed, almost like paint brush tufts.

Horses usually resent the scabs being removed as the skin below is sore and inflamed.


  • Fortunately, Dermatophilus bacteria are susceptible to most of the commonly used antibacterial solutions like iodine and chlorhexidine.
  • Because the bacteria live under the scabs it helps to remove the scabs gently before treatment.
  • They can first be softened with warm soap and water.
  • Then the antibacterial solution can be applied and left on for 5 to 10 minutes. A small soft nail brush is ideal for this.
  • The area should be rinsed and dried thoroughly with a clean towel, then an antibacterial ointment applied along with a moisture-repellent cream such as zinc oxide.
  • In very severe cases, antibiotic treatment by your vet may be needed.

Note: I have found that mild cases respond well to the simple application of lubricating oil, which softens the scabs so that they can readily be removed with minimum discomfort to the horse, and then the oil provides waterproof protection to the area while it heals.


  • If you know your horse is susceptible to mud fever, keep it off wet and muddy ground as much as possible.
  • Ensure there is always a clean dry area for it to graze and stand on.
  • You may need to fence off the very wet sections of the paddock and feed your horse out of the mud.
  • During long spells of wet weather apply an oil-based barrier cream to repel mud and moisture.
  • Avoid hosing the horse’s legs whenever you can, but if the skin gets wet dry the legs off gently and thoroughly with a towel.
  • Regularly check the skin of your horse’s lower legs and under its cover, and at the first sign of any scabs, treat immediately.

Mud fever and rain scald are persistent conditions and it can take time to treat them effectively. Once the bacteria have been destroyed, the skin needs to be protected from contact with wet and muddy conditions to allow healthy skin to grow back and heal properly.