I had a call from a client today with a great question - her horse had lots of little crusty bumps around his pasterns, and her farrier had told her it was probably "scratches". She called for more information about this condition, and what to do about it.
"Scratches" is also called "mud fever", "dew poisoning", or more medically appropriate "pastern dermatitis". "Derm" means skin, and "itis" means inflammation, so "dermatitis" just translates to "inflammation of the skin" which, in pastern dermatitis, occurs at the pastern. The term is descriptive, but it doesn't tell us anything about what causes it.
Essentially, when the skin around the lower limbs is exposed to constant moisture and mechanical irritation from long grass, mud or ice, it becomes damaged. Small cracks appear at the skin surface, which allows "opportunistic" bacteria and fungi to gain access. These microorganisms are normally present in the soil, but can't create an infection in normal, intact skin. They need the environment to irritate the skin sufficiently first. The infected skin then becomes thickened, crusted, and painful to the horse. There is often loss of hair along with the crusting.
Once these oppurtunistic skin infections take hold, they can be difficult to eradicate. The best way to help the skin heal is to remove the horse from the wet, muddy environment that is causing the primary irritation. This can be very difficult to do in some areas, but keeping the horse in a stall overnight, or putting down straw outside in muddy areas can help reduce some irritation.
The next thing to do is treat the infection topically. A simple scrub with dilute betadine or chlorhexidine scrub, rinsed well and dried, can be helpful. This again can be difficult to accomplish in very cold environments. Second best is usually a topical ointment such as Furazone or Nolvasan (Dermachlor). These ointments have antiseptic properties which can help kill both bacteria and fungus. They are best applied to clean skin/hair when the horse will stay out of the mud for at least a few hours (at the evening feed, if the horse is stalled at night).
Horses with thick "feathers" on their lower limbs are more prone to this condition, likely because the hair traps moisture. These horses may benefit from a light trim of the feathers, but don't shave the limbs completely - the thick hair is also protective.
Once the inflammation is under control, you can prevent further irritation by applying a thick cream, such as a diaper rash ointment or Corona (look for the ingredient lanolin) to the pastern area. This will repell moisture and help keep the skin soft and pliable, making it resistant to mechanical irritation.
If you are unable to control the infection yourself using topical treatments, it's definitely time to consult your veterinarian. "Dermatitis" can become "cellulitis", which is inflammation of the tissue beneath the skin. This condition can be difficult to treat, and recurrant in some horses. Sometimes systemic antibiotics are necessary, or an ointment that contains a steroid can be prescribed. We may recommend stall rest and bandages for a short period as well. If swelling begins to extend up the leg, if lameness is noted, or if the limb becomes very warm and painful, please call us as soon as possible.
If you have any questions about this condition or any other issue your horse may be having as we prepare for winter, please don't hesitate to call. Winter is a great time to get your questions answered quickly, since the appointment schedule lighter than in the spring. I look forward to hearing from you!