Sarcoids in Horses: A Complete Guide for Owners

Sarcoids are one of the most common types of skin tumours found in horses, ponies, and donkeys. Although they are non-malignant, meaning they do not spread to internal organs, they are locally invasive and can cause significant discomfort, disfigurement, and management challenges. Understanding how to recognise, diagnose, and treat sarcoids is essential for any responsible horse owner.

What Are Sarcoids?

Sarcoids are fibroblastic skin tumours, growths arising from fibroblasts, the cells responsible for producing connective tissue. They are classified as skin cancer, though they don’t metastasise to internal organs. Sarcoids can appear anywhere on the body, but they most commonly occur:

• Around the eyes and ears

• On the muzzle

• Between the forelegs or inside the thighs

• On the sheath, udder, or groin

• In areas of previous skin trauma or scarring

While sarcoids are not typically life-threatening, they can cause severe irritation, interfere with tack, attract flies, and become ulcerated or infected.

Causes and Transmission

The exact cause of sarcoids remains complex, but research strongly suggests a link with bovine papillomavirus (BPV types 1 and 2). The virus is believed to enter the horse’s skin through small wounds or abrasions and trigger abnormal fibroblast growth.

Transmission may occur via:

• Flies acting as mechanical carriers of the virus

• Direct contact with infected horses or contaminated equipment

• Trauma sites, such as wounds or scars, providing a route of entry

Some horses seem genetically predisposed, and stress or a weakened immune system may increase susceptibility.

Types of Sarcoids

Sarcoids present in several different forms, which can vary in appearance, growth rate, and response to treatment. The main types are:

1. Occult Sarcoids

• Flat, hairless patches with grey, scaly skin

• Often mistaken for ringworm or rub marks

• Usually found on the face, neck, or inner thighs

• May progress into more aggressive forms

2. Verrucose (Warty) Sarcoids

• Rough, wart-like texture with flaky or crusty skin

• Slow-growing and often dry

• Common on the face, neck, and body

3. Nodular Sarcoids

• Firm, round nodules beneath the skin or attached by a stalk

• Often found near the eyelids, groin, or sheath

• May ulcerate or become fly-struck

4. Fibroblastic Sarcoids

• Aggressive, fleshy growths that bleed easily

• Can ulcerate and spread rapidly if disturbed

• Often appear in moist regions such as the groin or inner thighs

5. Mixed Sarcoids

• Contain features of more than one type

• Can behave unpredictably and are harder to treat

6. Malevolent Sarcoids

• Rare but very aggressive

• Spread along lymphatic vessels under the skin, forming cords of tumours

• Difficult to treat and often carry a poor prognosis

Diagnosis

Veterinary examination is essential for an accurate diagnosis. While the appearance is often characteristic, biopsy may sometimes be needed. However, biopsies should be approached with caution, as disturbing a sarcoid can cause it to grow more aggressively.

Diagnosis typically involves:

• Visual inspection and history

• Fine needle aspirate (less invasive than full biopsy)

• Biopsy (only if necessary and followed by immediate treatment)

• Histopathology to confirm sarcoid type and rule out other skin conditions

Treatment Options

There is no single guaranteed cure for sarcoids, and each case must be assessed individually. The success of treatment depends on the type, location, and size of the sarcoid, as well as the horse’s overall health.

1. Surgical Removal

• Physically cutting out the tumour

• Best for small, isolated sarcoids in low-risk areas

• Risk of recurrence if any cells remain

2. Cryotherapy

• Freezing the sarcoid with liquid nitrogen to destroy tissue

• Often used after surgical debulking

• Multiple sessions may be needed

3. Laser Surgery

• Uses high-energy light to vaporise the tumour

• Minimises bleeding and reduces recurrence

• Requires specialist equipment and skill

4. Topical Treatments

Liverpool Cream (AW4-LUDES)

• A potent, veterinary-prescribed cytotoxic cream

• Developed at the University of Liverpool

• Applied under veterinary supervision only

• Highly effective but can cause inflammation and discomfort

Other topical agents

• Imiquimod (Aldara) – an immune response modifier for superficial sarcoids

• Bloodroot-based creams (Xxterra) – herbal but still potent; can be harsh and cause pain

5. Immunotherapy

• Involves stimulating the horse’s immune system to fight the tumour

• Techniques include:

  • BCG injections (mainly around the eye)

  • Autologous vaccines made from the horse’s own sarcoid tissue

  • DNA or viral vaccines (under research)

6. Chemotherapy

• Use of cytotoxic drugs such as cisplatin beads or injections directly into the sarcoid

• Often used for recurrent or difficult tumours

7. Radiotherapy

• Highly effective for sarcoids near sensitive areas (e.g., eyelids)

• Very expensive and only available at specialist centres

Management and Prevention

1. Early Detection

Inspect your horse regularly, especially in high-risk areas. Early treatment offers the best prognosis.

2. Avoid Trauma

Do not cut, rub, or pick at sarcoids. Avoid unnecessary friction from tack or rugs.

3. Fly Control

Use fly repellents, masks, and sheets to reduce the risk of transmission and irritation.

4. Hygiene and Biosecurity

• Disinfect grooming tools and tack shared between horses

• Avoid cross-contamination of wounds

5. Boosting Immunity

Good nutrition, stress management, and regular deworming can support the horse’s immune response.

Prognosis

The outcome depends on many factors. Some sarcoids remain static for years, while others grow rapidly or recur after treatment. Horses can live comfortably with sarcoids if properly managed, but vigilance is key. Recurrence is common, so follow-up checks are essential.

When to Call the Vet

You should seek veterinary advice if:

• A lump appears or changes in size, texture, or colour

• The sarcoid becomes ulcerated, painful, or bleeds

• Tack or flies irritate the affected area

• You are unsure whether a lesion is a sarcoid or something else

Conclusion

Sarcoids are the most common equine skin tumour and can appear anywhere on a horse’s body. While they are locally aggressive, they are not internally malignant, and with the right management, most horses can live long and healthy lives. The bovine papillomavirus plays a significant role in their development, and prevention focuses on fly control, wound management, and maintaining good hygiene.

Early veterinary assessment is crucial, as improper handling can cause a sarcoid to worsen. Treatment options are wide-ranging, from surgical removal and cryotherapy to topical or immunotherapy approaches, but none guarantee a permanent cure. Ongoing vigilance, good horse care, and close collaboration with your vet offer the best chance of controlling and minimising recurrence.

By staying informed and proactive, horse owners can manage sarcoids effectively and ensure their horses remain comfortable, healthy, and happy.