Sarcoids can be scary. These tumors can show up anywhere on a horse’s body and sometimes grow quickly, accounting for nine out of every 10 tumors seen in horses. They aren’t typically painful, but sarcoids often bleed if they’re bumped or scraped. They don’t spread throughout the body, but they can multiply and spread locally; these tumors tend to recur in the same location or nearby.

If the sarcoid is located in an area where it interferes with a horse’s ability to function well (like near his eyelid or sheath), or if it’s in an area where a halter, saddle or other tack rests, it may be necessary to investigate how to limit its growth or remove it entirely.

What Are Sarcoids in Horses?

The cause behind sarcoid development isn’t entirely clear, but there is strong evidence to suggest that the condition is instigated by a bovine papillomavirus, which is what makes these tumors so tricky to address. Sarcoids don’t behave like traditional tumors. There is also some indication that a genetic predisposition may be at play in the condition.

Any color, breed or gender of horse, donkey or equid can be affected by sarcoids, but young to middle-aged horses are most commonly affected. Sarcoids can be found across the globe, but there are some factors that may predispose horses to sarcoid formation, including the presence of cattle and flies, which may transmit the virus.

Sarcoids are made of abnormally dividing fibroblast cells, explains Elizabeth H. Yorke, DVM, Dipl. ACVS, of Springhill Equine Veterinary Clinic in Newberry, Fla. “They’re really common—actually the most common tumor horses get, with an estimated 2 percent of the equine population affected.”

Although sarcoids can become impressive in size and scope, they’re not usually regarded as life-threatening, explains Rana Bozorgmanesh, BVM, DACVIM, MRCVS of Steinbeck Peninsula Equine Clinics in Menlo Park, Calif. But it’s important to remember that what can be seen is the tip of the iceberg, she says.

Sarcoids infiltrate local tissue with fingerlike projections and are much more involved than what can be seen on the surface of the horse’s skin. Malevolent sarcoids, a particularly aggressive type of, spread along lymph vessels, according to Bozorgmanesh.

Sarcoids can occur nearly anywhere on the body, but there are some spots where they more commonly develop, says Yorke. These areas include on the face (especially around the eyes and ears), chest, groin, sheath, underside of the abdomen, inside the back legs and at sites of previous wounds, particularly on the legs. They can occur singly or in multiples; they can occur on one part of the body or over many sites.

What to Look For

It can be difficult to detect sarcoids in their beginning stages, and they can be well hidden in a horse’s coat. There are six different types, each with a different appearance.

“Sarcoids often look like warty, crusty, bumpy skin growths, but there’s a lot of variation in their appearance,” says Yorke. They can stay small for years, just looking like a grayish wart or a patch of bald skin, but then can start changing—and things can get ugly fast.

It’s important to have a vet peek at anything unusual on a horse’s body. While a small hairless patch may not necessitate a vet visit, having the vet take a look while she’s out for another reason (such as the spring wellness exam) is beneficial. The vet will be able to rule out other conditions and begin to develop a plan in case the sarcoid begins to grow.

As sarcoids enlarge, the skin can ulcerate, attract flies, and become infected, Yorke explains. They may look like open sores that won’t heal.

“Sarcoids can be very challenging to treat, so I recommend owners take them seriously, even if they don’t look like they’re currently causing a problem,” she says.

What are the Treatment Options for a Horse with Sarcoids?

Sarcoids are only positively diagnosed with a biopsy. Once a vet has confirmed that the horse has a sarcoid, there are multiple therapies that can be used to combat the condition, some of which may be used in combination.

“There are so many factors to consider when deciding on a treatment protocol, including the type of sarcoid, how aggressive it is, its location and size, how well the horse is likely to tolerate a particular treatment, cosmetic outcome and more,” says Bozorgmanesh.

Also taken into consideration are location of equine clinics (should in-hospital surgery be warranted) and the client’s financial capability.

In the past, horse owners were encouraged to leave a sarcoid alone unless it was growing or changing, but as sarcoid treatments have evolved, it’s been recognized that early intervention may be more successful.

“It’s easier to treat small sarcoids, and less-aggressive treatments may also be an option if the lesions are caught early,” says Yorke. It’s very rare for a sarcoid to go away on its own.

Because they are caused by a virus, treatment is not as simple as just cutting off the tumor, she adds.

“Unfortunately, even if all the tissue that looks like sarcoid is surgically removed, the ‘normal’ looking tissue adjacent to it can still be infected by the virus, and it can then be activated into new sarcoid tissue,” Yorke notes. “It’s very important that your equine veterinarian is consulted to create a treatment plan. Inappropriate treatment can quickly turn a small lesion into a larger and more aggressive one. So please don’t buy some ‘cure-all cream’ off the internet to treat your horse’s sarcoid—you may regret it later.”

Treatment options can include:

◆ Veterinary-grade topical ointments: There are a variety of options available, and you can apply it yourself; you’ll have to wear gloves and put it on every few days. However, it can take up to 32 weeks of treatment for the sarcoid to resolve, and some horses may experience a burning sensation when it’s applied, says Bozorgmanesh.

◆ Injection of chemotherapy into the tumor: Injecting cisplatin, a chemotherapy agent, is one of the most successful ways to treat sarcoids. If the tumor is large, the vet will often try to surgically remove as much of the tumor as possible before treating the scar line and the tissues around it with cisplatin, Bozorgmanesh explains. The injections are often repeated every two to three weeks for four to six treatments. Depending on the location, this treatment may need to be done under general anesthesia.

◆ Injection of immune modulators into the tumor: Immunomodulators are natural or synthetic substances that can modify the body’s immune response by either suppressing or stimulating the immune system.

◆ Injection of immunostimulants into the tumor: A newer treatment for sarcoids, this modality focuses on increasing specific aspects of the immune system and its response. It has variable success.

◆ Surgery: When removing a sarcoid, the vet must excise large amounts of tissue in an attempt to remove every single tumor cell. Tumors often recur when using surgery alone.

◆ Cryotherapy: Extreme cold is used to freeze and remove abnormal tissue. This modality can require multiple treatments and may require general anesthesia.

◆ Lasers: A surgical laser is used to remove the tumor, along with a margin of healthy tissue to reduce the chance of leaving behind any potential cancerous cells. This technique may require general anesthesia or local anesthesia and sedation, says Bozorgmanesh.

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There are also some specialty treatments like electrochemotherapy or radiation that can be very effective but are usually performed only at veterinary schools and require general anesthesia, according to Yorke.

“It’s also important to remember that any treatment may have to be changed or repeated if the sarcoid doesn’t respond well or comes back later,” she says. “That’s just the nature of sarcoids, and can happen despite everyone’s best efforts.”

The bottom line? Anytime something unusual is found on a horse, it’s worthwhile to have a vet take a peek at it to be sure nothing is amiss. Addressing sarcoids early offers horses the best chance for a complete resolution.

This article about sarcoids in horses appeared in the May 2023 issue of Horse Illustrated magazine. Click here to subscribe!

These Horse Care Tips are presented by CareCredit.

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If you live in an area where sunlight is plentiful and horses spend hours outside, you’ve most likely seen white faces turn pink as warmer weather takes hold. Like humans, horses are susceptible to sunburn, which occurs when skin is exposed to too much ultraviolet (UV) light. Horses most likely to be affected by too much sun are those with white hair/pink skin on their faces and large swaths of white or lighter colors on their bodies, like Paint Horses and Appaloosas. Though most of us are familiar with sunburn and its manifestation in horses, there is an equine condition that causes what looks like sunburn on steroids, called photosensitization, or photosensitivity.

Photosensitization occurs when certain photodynamic compounds in the skin are exposed to sunlight, which causes a chemical reaction that damages cells. The injured area will become ulcerated, fluid-filled and painful. Like sunburn, this condition often affects areas on the horse that are lightly pigmented and have sparse hair covering, like the muzzle, eyes, tips of ears, and base of the tail.

There are multiple types of photosensitivity; the type a horse is experiencing is classified by the source of the photodynamic compound. The kinds that most often impact horses are systemic photosensitivity (often called primary photosensitivity) and hepatogenous sensitivity (also called secondary photosensitivity).

No matter the cause, the signs of photosensitivity are similar, though the time between exposure and onset of signs may vary.

Feel the Burn

Photosensitization is often seen in summer months when sunlight is most intense and pasture grasses are thriving. Mild photosensitization or cases in early stages may be difficult to discern from sunburn, but advanced cases are easy to recognize.

Light and white areas of the horse affected by photosensitivity can often be so damaged that an owner may worry that the horse got tangled in something, like a wire fence. The skin can be red and blistered, as well as swollen and hot to the touch. Photosensitivity on the legs can also look like scratches (also known as dew poisoning, mud fever, greasy heel or pastern dermatitis).

The blisters eventually break, leaving oozing, raw areas that will become crusty and eventually peel away. Horses experiencing photosensitivity may rub or scratch affected areas, further damaging skin. The wounds can easily become infected without diligent care.

Substances that cause photosensitization can be found in plants and drugs; some chemicals may also act photosensitizing agents. For horses, the compounds most often to blame are plant-derived.

Primary Photosensitivity in Horses

Primary photosensitivity takes place when a photodynamic agent has been ingested by the horse or injected into his body or absorbed through the skin. The agent then circulates throughout the bloodstream, but only causes skin cell damage when the horse is exposed to UV light.

One common pasture plant containing a toxin that can cause primary photosensitivity is alsike clover (Trifolium hybridum), which looks similar to red clover (Trifolium pretense) or white clover (Trifolium repens). Red and white clover are purposely planted for hay and pasture, so it’s important to identify which is which.

Other plants that can cause primary photosensitization are buckwheat, oatgrass, perennial ryegrass and St. John’s wort.

Many other plants (including other clovers and Bermudagrass) are suspected to cause primary photosensitization, but the specific toxins have not yet been identified. Hay made from any plants that cause photosensitivity may also cause a reaction, as the toxins are not destroyed by drying.

Certain drugs can also cause photosensitization, so a conversation with your horse’s veterinarian may be warranted if he is on any of the following: phenothiazine, some sulfonamides (like trimethoprim sulfa), and tetracycline.

Secondary Photosensitivity in Horses

Secondary photosensitivity is the most common photosensitivity found in horses; it takes place when a horse’s liver is compromised to the point where he can’t metabolize specific chemicals normally.

Liver damage can be caused by a myriad of things, but this type of photosensitivity often occurs when a horse ingests plants or blue-green algae that damage the liver, affecting its ability to remove photodynamic compounds from the bloodstream.

Horses most at risk of this type of photosensitization are turned out on pastures that are overgrazed and in poor condition. Oftentimes, more than one horse in a field will be affected by secondary photosensitization.

Some plants can cause both primary and secondary photosensitivity, but the more profound toxic effects, such as liver damage, come from the ingestion of plants that contain pyrrolizidine alkaloids (PAs). Plants with higher levels of PAs include buttercup, comfrey, heliotrope, kale, lanata and ragwort, among many others.

You should call a vet if your horse has no appetite, is lethargic or jaundiced, or is in poor body condition in addition to being sensitive to sunlight; these are all signs of liver damage. Additional diagnostic testing may be necessary to determine how impaired liver function is.

Treatment of Photosensitization

Treatment of the wounds caused by photosensitization is often simply management of symptoms while allowing the skin to heal. Horses experiencing photosensitization should be kept out of the sun and preferably off the pasture that caused the photosensitive reaction. The wounded area should be kept as clean as possible to minimize secondary skin infections, and it is critical to keep flies at bay.

Gentle cleaning of the affected area is recommended; scabs covering the damaged skin should be left alone because picking or removing them could prolong healing and encourage infection. A vet may prescribe steroids to relieve some of the inflammation or an antibiotic if the infection is severe.

Prevention of Photosensitization

Owners of horses with lots of chrome should be diligent in their assessment of white legs and faces (as well as bodies). It’s much easier to heal lesions caused by photosensitivity if the wounds are caught early, but it’s even better to keep sun-related injuries at bay. Try the following:

◆ Use a child-safe sunblock on the areas of the horse that are likely to burn, like around noses and eyes. As always, the higher the SPF number, the more protection the product will offer.

◆ Apply a diaper rash cream, which contains zinc oxide. The sticky product often stays in place longer than traditional sunscreens when the horse grazes in taller grass. An added bonus: These creams are so thick that an owner can tell if a spot was missed during application and bare skin remains exposed.

◆ Consider using shampoos, coat care products and fly sprays that tout their ability to help block sunlight. Remember that these products may not adequately protect a horse’s skin when used alone.

◆ Use fly masks with ear or muzzle coverings; if using a fly sheet or fly boots, opt for products with UV protection.

The wounds and pain caused by photosensitization can be significant and the healing process arduous. Though the cause may never be clear, the owner of any horse who has experienced a photosensitive episode will remain diligent in their monitoring of white patches to try to prevent it from happening again.

Removing Common Culprits of Photosensitization

Alsike clover and St. John’s wort are common causes of photosensitivity in horses, and their management in fields can be key to preventing repeat occurrences.

If alsike clover hasn’t taken over a field, it can be sprayed or removed by hand. However, if the pasture is infested, complete renovation should be considered to prevent the ongoing ingestion of the plant by horses.

St. John’s Wort spreads both by seed and underground rhizome, so it can be difficult to eradicate manually or with herbicide application. It’s also resistant to many herbicides, so a call to your local extension agent may be needed to get advice on how to eliminate it from fields. Biological controls like flea beetles, moths and midges have been used to kill St. John’s Wort, as they ingest the foliage but don’t harm other pasture grasses.

If you suspect a problem or the wounds have gotten severe, contact your vet for advice on an immediate treatment protocol.

This article about photosensitivity in horses appeared in the July 2022 issue of Horse Illustrated magazine. Click here to subscribe!

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That’s why it’s crucial for horse owners to learn to identify the causes and clinical signs of common dermatitis. By educating yourself about them, you can quickly and correctly treat the problem. Your horse will thank you!

A Healthy Skin Barrier

According to Rosanna Marsella, DVM, a veterinary dermatologist at the University of Florida in Gainesville, Fla., the key to preventing many problematic skin conditions is to protect your horse’s skin from trauma.

Grooming your horse on a daily basis can help keep your horse’s skin and hair healthy, but it’s also important to provide horses with adequate shelter from the elements, as well as protection from biting insects. When trauma occurs to the skin, your horse becomes more susceptible to bacterial or fungal infections.

“Animals who are immunosuppressed, or out in the rain day in and day out, or getting bitten by bugs, experience more trauma to the skin,” Marsella explains. “If the skin has no insect bites and the horse isn’t itchy and rubbing himself on a tree, for example, then the integrity of the skin barrier remains intact.”

Fight Flies

In addition to practicing good grooming habits to keep your horse’s skin and hair healthy, invest in a good fly product to prevent bites.

“Use of effective fly repellent is key, and that’s actually a topic that frequently confuses many people,” says Marsella. “The labels on some products may make them sound like repellents when they’re actually insecticides. If you spray an insecticide directly on an insect, it dies. But insecticide doesn’t prevent the insect from actually landing on the horse. That’s why you need to use repellent.”

When you’re looking for fly repellent, Marsella recommends checking the active ingredient listed as well as the percentage of the active ingredient.

“One example is permethrin,” she says. “In order to be a repellent, a fly spray product has to be at least 0.5 or 1 percent permethrin. But if a product only has 0.1 percent permethrin, then it’s not a repellent.”

For horses who may be allergic to chemicals, Marsella recommends trying botanical products, such as neem oil.

“Neem oil is a demonstrated repellent against mosquitos and no-see-ums,” says Marsella.

There’s another benefit to a daily routine of grooming and using fly repellent. By laying your hands on your horse every day, you’ll learn what’s normal for him and what’s not. Then you can spot skin issues in the making before they ever become full-blown problems.
There are many different skin conditions in horses, often with multiple contributing factors. Some horses can develop secondary issues, such as staph infections, which may require prolonged medical treatment from a veterinarian. If you suspect your horse is developing a skin condition, call your vet immediately.

Cannon Crud Cannon keratosis is often used to refer to “cannon crud,” or the development of flaky skin and oily build-up of keratin on the front of the cannon bones. But there’s also a genetic condition known as primary cannon keratosis. “Primary cannon keratosis is not common,” says Rosanna Marsella, DVM, a veterinary dermatologist at the University of Florida in Gainesville, Fla. “There are some horses that are genetically prone to this disease. The skin has a different way of maturing in some body areas, including on the cannon bone. This is not an infection. Horses with primary cannon keratosis will be genetically prone to it, and they will always have a little bit of crusty skin in that area. The treatment is management using shampoos to soften and loosen up the scabs. These horses can also get keratosis on their sides or chest.” For the non-genetic form of cannon keratosis, gently groom your horse’s legs with a curry comb and wash with an keratolytic shampoo to help manage crusty scabs and flaky skin.

Rain Rot

Rain rot is caused by the bacterium Dermatophilus congolensis. Characterized by small, round scabs crowned with matted hair, rain rot lesions typically develop along the topline of the horse.

“The development of the disease is precipitated by moisture, which is why we call it ‘rain rot,’” says Marsella. “It’s common in animals who are immunosuppressed or out in the rain and bitten by insects. Dermatophilus can access the skin when there’s trauma. Don’t pick at the scabs, because it’s painful for your horse and also delays healing. When the scabs are ready and the skin underneath is healthy, the scabs will come off on their own. But pulling a scab off and leaving a raw spot is never the answer.”

Rain rot is contagious and zoonotic, which means that other horses and humans can contract the condition. Marsella recommends treating rain rot with an antimicrobial shampoo, such as chlorhexidine or benzoyl peroxide.

“People can be overzealous and like to scrub at the lesions, because they think it will speed up the recovery, but the single most important thing is contact time,” says Marsella. “Apply the shampoo, gently massage it in, and then set your clock for 10 minutes and go do something else. Then come back and rinse. Contact time is what really makes the difference.”

Scratches

Pastern dermatitis, or scratches, is a name for a clinical syndrome, rather than a specific disease. Another common name for scratches is “dew poisoning.” Pastern dermatitis refers to the development of scabby areas on or near the pasterns. Two of the most common causes of pastern dermatitis include bacterial infections and mange.

“Pastern dermatitis can be caused by a lot of different things, including allergies, auto-immune diseases, staph infections or vasculitis,” Marsella explains. “It’s common on horses with white legs or horses with feathers. When an owner has a horse with pastern dermatitis, they can use an anti-microbial shampoo because there’s probably an overgrowth of bacteria.”

In addition to treating for bacteria, owners can protect horses with white legs from pastern dermatitis by covering the legs with socks or wraps.

“Products like antimicrobial silver socks may help, but more importantly, the sock also protects the skin from UV exposure,” says Marsella. “Vasculitis is triggered by UV rays. You can either put socks on your horse or keep him inside during the day and turned out at night. Many cases of pastern dermatitis also have an insect component, so it’s important to use repellent.”

Mites can also cause pastern dermatitis in horses with feathers. Mites can spread from horse to horse and can also survive in the environment for several weeks.

“Feathered horses are prone to mites, and they get very itchy legs as a result,” says Marsella. “Some horses may become itchier than others because they develop allergies to the mites. When you have mites, you’ve got mange. To treat mange, you have to kill the mites with a treatment like a lime sulfur dip. If a horse is diagnosed with mites, everybody in contact has to get treated whether they’re symptomatic or not. The life cycle of the mite is three weeks, so treatment has to be at least that long.”

Ringworm

Ringworm is a common skin infection caused by a fungus, not a parasite. Ringworm presents as round, raised lesions on the skin that may be itchy.

“They call it ‘ringworm’ because it will develop a round lesion on the skin, but it’s actually caused by a fungus,” Marsella explains. “It is transmissible, so you need to treat the horse for it.”

Ringworm can be transmitted from horse to horse by direct contact or by sharing infected tack, brushes, clothing or other equipment between horses. Marsella recommends using an antifungal treatment, such as a lime sulfur dip, to treat ringworm.

“Lime sulfur is very effective at killing fungi and helps with the itching,” says Marsella. “It will also kill mites.”

Dealing with any kind of skin condition—especially before it gets out of hand—not only allows your horse to look his best, but it helps him stay comfortable, happy, and itch-free.

This article about equine dermatitis appeared in the September 2020 issue of Horse Illustrated magazine. Click here to subscribe!

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