31 Mar Scratches
“Scratches”, “mud fever”, and “greasy heel” are all familiar terms for pastern dermatitis, a common equine skin problem. Technically, pastern dermatitis is not a single disease but a generic skin reaction to a variety of causes. The skin irritation is most often visible at the back of the pasterns and heels, but can sometimes extend along the entire lower limb. Initially signs may be limited to redness and scaling, but they often progress to oozing of fluid (serum) from the skin, matting of hair, and development of crusts. Chronic cases can become very ugly indeed, as the skin becomes thickened and swollen. It may even develop bumpy, mass-like tissue. This condition is very painful for the horse, and can cause lameness in some cases.
“Scratches” is most commonly seen on white-colored hind legs of all breeds of horses. It can be unilateral (one sided), or bilateral (involving both right and left limbs). It may affect all four legs. Most cases seen in our region are due to bacterial folliculitis (bacterial infection), but other causes include contact irritation from caustic substances, mites, fungal infection, and photosensitization related to pasture plant toxicity. In some drafts (Clydesdales and Shires), an immune-mediated problem is suspected which may have a genetic component. Some individuals seem particularly susceptible to pastern dermatitis, so these horses should be monitored carefully at wet times of the year and treatment should begin at the very first sign of inflammation.
Excessive moisture or wet-dry cycling in the horse’s environment seem to be significant predisposing factors, so prevention should be geared toward keeping the legs clean and dry. Susceptible horses can be stalled during wet weather or until the morning dew has dried. Clipping hairs, especially feathers, can also help decrease moisture retention. Maintain pastures, paddocks, and sheds with the goal of reducing deep mud and standing water. This is not always easy in Western New York!
When pastern dermatitis has been diagnosed, we usually begin treatment by clipping the hair from the area, and then start with topical remedies. The area should be washed with warm water and a gentle soap such as chlorhexidine (Nolvasan™) or betadine surgical scrub. After scabs are softened by the soap, they should picked off in order to expose the underlying skin. Be careful, you might get kicked if you are not gentle! After rinsing, the skin should be completely dried before topical medications are applied. Excema ointment, specially formulated at the Genesee Valley Equine Clinic, is usually our first choice. This ointment is a combination of nitrofurazone, zinc oxide, and a small amount of steroid. It provides an anti-bacterial, an anti-inflammatory, and a moisture barrier. Anti-inflammatory drugs like Bute or Banamine™ are also prescribed if the horse is uncomfortable. In stubborn cases, systemic antibiotics or steroids may be necessary to provide relief. Recurrence is common, especially if the underlying cause is not addressed, so it is worth seeking a definitive diagnosis!