Equine pastern dermatitis—better known as scratches—is a condition most horse owners and grooms will battle at some point, whether they care for backyard ponies or million-dollar equines. The crusty scabs may start as a minor annoyance, but if left untreated they can lead to swelling, inflammation and lameness, or even become a chronic condition.

Equine pastern dermatitis or “scratches” often presents as inflammation and scabbing on the back of a horse’s lower legs. Most cases can be treated at home. Arnd Bronkhorst for Arnd.nl Photo

Nimet Browne, DVM, DACVIM, an internal medicine specialist at Hagyard Equine Medical Institute in Lexington, Kentucky, wrote a paper on common equine skin conditions for the American Association of Equine Practitioners Spur Of The Moment news bulletin in 2018.  She answered some frequently asked questions about equine pasture dermatitis and its cure.

What Causes Scratches?
Scratches is a term used to describe the effects of a skin infection caused by microbes that thrive in wet, dirty conditions. It’s commonly assumed to be a fungal infection, but Browne said that’s not entirely correct.

“Although fungus can play a role in scratches, the primary concern and the most common cause of scratches is bacterial,” she said. “Typically we don’t know exactly what causes [scratches.] In general, it’s multifactorial in nature, so what causes it isn’t necessarily the thing that perpetuates it. Often we see something like a bacterial infection that is allowed to set up because of a break in the skin barrier, and then maybe in addition there’s a fungal component. Sometimes we can localize it to a certain bacteria or fungal infection, but it has a pretty classic appearance of reddening, scaling, sometimes even oozing.”

Any horse exposed to wet, dirty conditions like muddy turnout is at risk, but there are some additional factors that may make a horse more likely to develop scratches.

“We don’t know for sure that there’s a genetic component, but the horses that get the most severe form of scratches like the draft breeds or breeds that have feathers on their pasterns and fetlocks seem to be predisposed,” Browne said.

Trauma can also increase a horse’s chances of developing scratches. Any break in the skin around the fetlocks or pasterns, whether it’s a rub from a bell boot or a nick from clippers, makes it easier for bacteria to invade. White legs or legs with large white makings also seem more susceptible

An Ounce Of Prevention
Most cases of scratches resolve if you can remove the horse from the wet environment and keep its legs clean and dry, but there are also topical options. When purchasing over-the-counter products to treat scratches, Brown suggested looking for a few key ingredients.

“Because there’s not always one cause, we do look for a treatment that’s a multi-pronged approach with antibacterials, antifungals and anti-inflammatories as well,” she said. “So an antibacterial, like Betadine, then maybe an antifungal, which usually has ‘azole’ at the end, tends to be the most efficacious. Some topical ointments or shampoos also have anti-inflammatory properties – either a steroid or an antihistamine. Something to help wick water away helps too, like petroleum jelly. We have some evidence that giving Omega 3 fatty acids can help with any skin disease. [Omega 3 fatty acids are in] a lot of supplements these days and can be beneficial for their anti-inflammatory properties and improve the overall dermatologic health of the horse.”

Some cases of scratches do require antibiotics or additional veterinary intervention. The condition can be painful and may cause significant swelling or lameness. Browne advised that if the condition gets worse with treatment, or if the horse exhibits other signs of illness such as fever or lethargy, or develops lesions on other parts of its body, it’s time to call a professional. A veterinarian’s response will differ based on the severity and underlying cause.

“We look for the underlying factors: skin mites, bacteria, fungal infection,” said Browne. “And we’d do a skin scrape looking for the infectious causes, then treat those directly with antibiotics or antifungals. If we don’t find any of those, the best treatment is the same as what the owner can do – a clean, dry environment with topical treatments.”

Fact or Fiction?
– Clipping a horse’s legs prevents scratches.
Fact, but there’s a catch.
“It’s a double-edged sword, because removing hair from the legs does make it easier to keep the area clean and dry, especially if your horse has feathers,” Browne said. “The other side of that is we want to be careful not to damage the skin’s surface. The skin – when it’s intact – has a lot of protective measures against infection. If we break that we can actually set up horses to develop scratches.”

– Washing a horse’s legs too often will make scratches worse.
Fiction.
Browne suggested washing a horse’s legs as often as daily to keep them clean. If a horse is affected by scratches, a shampoo with antibacterial or antifungal properties might help speed healing, but the most important thing is to dry the legs completely after bathing. This is especially important if the horse will go into a stall after a bath, or have any kind of boot or wrap put on that might trap moisture close to the skin.

– You should pick off the scabs.
Partial Fact.
Browne advised only removing scabs that are already falling off or come off with normal cleaning.

“Don’t scrub until it’s bleeding,” she said. “But if you’re washing with a glove or mitt, taking off anything that comes easily and doesn’t cause pain or irritation to the horse is appropriate. The more debris in the area, the more bacteria, fungi or dirt can stay there. The goal is to get that off to treat the underlying problem.”

This article appeared in the October 7 & 14, 2019 issue of The Chronicle of the Horse as part of our Fall Horse Care issue.

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