By Justin High, DVM

Horses are wonderful creatures with an innate sense of beauty that is unlike any other in the animal world. So, when a group of single-celled organisms, like bacteria or a fungus, gets the upper hand on them, it doesn’t seem quite right. Pastern dermatitis is an excellent example of this, and one we all face eventually.

Pastern dermatitis goes by many names, most commonly “scratches” or “dew poisoning.” Other folks call it “grease heel” or “grapes,” depending on the severity of the case. Scratches often starts innocently enough, but can proceed to a debilitating state where horses can hardly walk, let alone work.

Equine pastern dermatitis is not actually a single disease, but a morphologic description of what is going on. It basically describes a skin reaction pattern in horses. Typically, the hind limbs are affected more so than the fore limbs, with the condition usually being bilateral. Virtually any breed and type of horse is susceptible.

There are three basic forms of equine pastern dermatitis: 1) Mild Form – the most common, where the lesions appear dry and crusty, with hair loss and scaling of red, irritated skin. Pain and sensitivity vary depending on the case. 2) Exudative Form – lesions have progressed to being very painful and red, with erosions of the skin and obvious blood-tinged or pus-like drainage. 3) Chronic Proliferative Form – “proud flesh” or granulation tissue has formed that has become dried and cracked in appearance, producing a scar-like surface.

Unfortunately, some horses are genetically predisposed to develop scratches. Ones with nonpigmented skin and hair on the pasterns, feathers in draft breeds and those with skin disorders will inevitably be affected. Others are brought into the group by environmental factors, such as a moist climate, consistently dirty stalls and bedding, alkaline soils, and sandy turnouts and pastures. The rest are victims of our own poor grooming habits, ill-fitting leg wraps and irritating topical leg products.

Without question, the most common cause of scratches I see in daily practice is a horse that is worked in a deep training pen wearing hind support wraps and is then returned to a deeply bedded stall while he’s still wet from being bathed. His pasterns are already irritated from sand getting in even the best-fitting boot and then ground around by stops, turns and rollbacks during training. Then, while he is still wet from a well-intended bath, he stands tied in a stall with shavings, that have a fairly high bacteria count even when routinely cleaned, up to his fetlocks. You can see how opportunity meets with preparation to produce the infection.

Diagnostically, the best way to address a case of scratches is to do a good physical examination of the entire horse, paying close attention to the recent history to help determine as many predisposing, primary or perpetuating factors as possible. Evaluating the degree of lameness and sensitivity is a good starting point, but the best way to effectively treat scratches is to get the right diagnosis.

Skin scrapings and microscopic evaluation of cells obtained from the damaged skin help to identify bacteria, fungi, inflammatory cells and even parasites, such as chorioptic mange mites and chiggers. The most common bacterial infectious agents I see are Staphylococcus and Dermatophilus, but fungal organisms and budding yeast are routine agents that produce mixed infections that can prove difficult to treat. In recurrent cases or when a horse is responding poorly to appropriate therapy, biopsy of the affected tissue is warranted.

For horses with scratches, barn management is every bit as important as treatment. Not turning horses out in the morning until the dew burns off, avoiding consistently muddy pastures, keeping horses out of deep, sandy areas, clipping excessive feathers on hind fetlocks, and keeping stalls as dry and clean as possible are solid ways to prevent lesions. For existing cases, start by clipping the hair off the affected area, scrub the scabs completely off with antiseptic soap (chlorhexidine or iodine scrub), and be sure to allow the skin to fully air dry before returning the horse to a pasture or stall. Mild cases need no more treatment than this, which almost any horse owner can do. For problematic cases or those folks who do not enjoy picking scabs, like me, call your veterinarian as soon as possible to get ahead of the problem.

There are almost as many secret remedies for scratches as there are causes, and as you can imagine, I have my own “special formulation.” But they all more or less revolve around treating infection and suppressing inflammation, while promoting healing and soundness. Trust me, that is much easier said than done. After 15 years of refining my formulation, I believe I’m there, but it’s kind of like the “veterinary CIA” – if I told you what’s in it, I’d have to kill you.

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Dr. Justin High is a veterinarian and partner in Reata Equine Hospital in Weatherford, Texas. He graduated vet school from Texas A&M University and completed an internship at The Littleton Equine Medical Center in Denver, Colo. High’s years of practice focuses on the Western performances horse. Send any comments or questions to [email protected].