At one time or another, many horse owners have experienced the frustration of trying to clear up that red, scabby, oozing, irritated skin inflammation on the back of their horses’ pasterns. Known by a variety of names such as dew poisoning, mud fever, and scratches, the condition is common when horses spend time walking through damp pasture grass, but it can also be found in arid climates where the horses are kept in drylots. Sometimes the condition is fairly mild and doesn’t seem to bother the horse, but a bad case can cause bleeding, pain, and lameness. Repeated irritation leads to scaling, scarring, and thickened skin.
The skin on the sides and back of the pastern is constantly exposed to dirt, manure, urine droplets, moisture, and contact with plant leaves and stems. The area can be injured if the horse bangs or runs into rocks or tough plant material. Additional dangers include kicks from other horses or the horse stepping on or kicking itself as it moves around. Dampness allows dirt to stick to the skin, and any small injury allows bacteria to enter even if the skin is dry. In some draft breeds, thick and long pastern hair retains moisture and blocks sunlight, making these horses more susceptible to skin problems. All these factors put the pastern area at greater risk than skin on other parts of the horse.
In a herd of several horses sharing the same pasture, it’s not uncommon for one or two to be affected while the rest are not bothered. Because all share the same surroundings, individual risk must be higher for some horses than for others due to factors that are not well understood. Owners of horses with white or light-colored pasterns sometimes feel their horses are more inclined to be affected, and experts have found evidence that some draft breeds have a genetic predilection to severe pastern irritation.
Pastern dermatitis can originate from a variety of factors, and identifying the cause is the first step in treatment. A veterinarian uses techniques such as visual examination, information about the horse’s health history, skin scrapings, fungal cultures, and tissue biopsies to find out whether the irritation is caused by bacteria, fungi, or some type of parasite such as skin mites. In some cases, more than one factor is involved, and treatment will need to target all causes. Depending on the veterinarian’s findings, use of the proper medications may help to clear up pastern dermatitis, though some cases can be incredibly stubborn.
Once the broken skin has healed, owners may be advised to keep the area clean and dry to prevent reinfection. For horses at pasture, this is easier said than done, and oil-based ointments might be prescribed to coat and protect the at-risk areas.