19th November 2023

What are Sarcoids?

Sarcoids are a relatively common tumour seen in horses of all kinds. although they generally cause no major health problems because they are limited to spreading on the skin alone, the presence of sarcoids can cause irritation, problems with tack and a loss of value if selling your horse.

It is believed that sarcoids are caused by a virus spread between horses by flies which takes advantage of small wounds in your horse’s skin. They are seen most commonly around eyes, ears, chest, the belly and the lower limbs. Some horses may only have one sarcoid whilst others may have several across their body.

How do I recognise a sarcoid on my horse?

Sarcoids can present in a number of different ways:

  • Occult – Flat, hairless areas of dry, thickened, hairless skin
  • Nodular - rounded often hairless lumps
  • Fibroblastic - can appear like a wound that doesn’t heal as expected.
  • Verrucous - Wart like lump
  • Malevolent - can spread along the skin causing a chain of lumps and ulcers.
  • Mixed

Sarcoids are usually only small but can grow over 10cm in some cases. Some appear very similar to other skin tumours seen in horses. If in doubt, ask your vet to take a biopsy (sample) or remove the whole tumour to send for identification at a lab.

Commonly, sarcoids can become ulcerated and bleed if rubbed or knocked and this can cause irritation, localise infection and pain (with or without swelling) and they are also a source of fly-worry. Sarcoid transformation at a wound site can occur and is a very serious cause for a wound to heal slowly. This occurs when a horse with sarcoids sustains a wound (trauma etc.) and goes on to develop a sarcoid at the wound site. The appearance is very similar to exuberant granulation tissue (“proud flesh”). If any wound is failing to heal as expected, particularly on the limbs, sarcoid transformation should be considered.

What horses get sarcoids?

Sarcoids can affect any horse, pony, donkey or mule (also Zebras and Przewalski horses!). They can develop at any age, and they occur everywhere around the world. There is no sex predilection (i.e. no sex is predisposed to getting them), coat colour has no effect, but some breeds do seem to be more susceptible, as do some families of horses, which shows there is a genetic susceptibility in some horses. There are many factors which influence the development of sarcoids, but we do not fully know what these all are.

What causes sarcoids?

There is debate over the cause, although there is some evidence that a viral antigen may be the underlying cause. It is thought that viral elements in cells change the behaviour of the fibroblasts at certain sites causing proliferation which can result in a visible tumour. Some horses are genetically more susceptible to getting sarcoids.

How do I stop my horse getting sarcoids?

There is no reliable way to avoid sarcoids. Reducing contact with flies using fly repellent and fly rugs may help to reduce spread. It is also important to keep wounds clean and protected to avoid them becoming a target for flies.

How do we diagnose sarcoids?

A vet should be consulted early if you suspect your horse has a sarcoid. Many are easily diagnosed tentatively based on a visual examination, whereas in others a small biopsy and histology may be required to diagnose, or to confirm a preliminary diagnosis.

How can sarcoids be treated?

Several different types of treatment exist for sarcoids, and more than one may be used at a time depending on the type and location of the lesions. The tumours are easier to remove when they are small. However, there is a high risk of recurrence and sometimes issues with healing following removal.

Options for treatment include:

  • Laser Surgery: Our most common and most success treatment is to remove the sarcoids using a laser. A laser is used to cut away the bulk of the sarcoid and cauterise the resulting wound at the same time.

  • Surgical Removal: Small tumours can be removed using local anaesthetic and sedation to cut around the lump and remove it. Depending on location and number of lesions it may be safer and more effective to remove the sarcoids under a general anaesthetic. The resulting wound will either be sutured or left to heal depending on its size. Following removal alone around 50% of sarcoids will reoccur.

  • Ligating With Rubber Rings: This only works on sarcoids which stick outwards and often doesn’t remove the whole of the tumour. A tight band is applied around the tumour cutting off the blood supply. After a few days the part of the tumour with no blood supply will fall off.

  • Freezing: This causes the tissue to die away. If the sarcoid is large the bulk of it should be removed surgically first. There is less recurrence this way but scarring is likely to happen

  • Chemotherapy: Skin killing creams can be prescribed by a vet to apply onto sarcoids. They can be very effective but care must be taken as they will also attack healthy skin and can do a lot of damage, particularly if applied over blood vessels. The creams will also damage your skin if you come into direct contact with them. Injections of skin killing chemicals can also be used alongside surgery.

  • Radiation Therapy. Specialised equipment is used to apply a dose of radiation directly to the sarcoid. This method carries some risk to the person applying the radiation so your vet would have to have undergone extra training to use this method.

Discussing the options with your vet is very important to find the right treatment for you and your horse.

Can we prevent sarcoids?

  • Any wound on a horse which has a sarcoid at another site must be promptly dealt with, including veterinary input as soon as possible.
  • It is still not clear as to how transmissible sarcoids are between horses, but it is common sense to exhibit caution, particularly during summer months, with regards to general fly control particularly when a horse has a wound and is co-grazing with another horse which has sarcoids.
  • There is currently no vaccine to prevent sarcoids and it is unlikely that there will be one in the near future, despite research efforts.
  • Any horse which has sarcoids must be monitored regularly for signs of progression.

Should I buy a horse with sarcoids?

There are many considerations to buying a horse with sarcoids. Many small sarcoids do not interfere with the horse’s work but they all have the potential for progression. The location of the sarcoids is important as if they are in an area, which is easily abraded/interfered with by tack, then this can reduce the ability of the horse or pony to perform as required. However, smaller, flatter sarcoids may not interfere with ridden work. A brood mare with sarcoids on her udder may resent a foal feeding from her udder. The other main consideration is expense and possible consequences on insurance for veterinary cover. Treatment of sarcoids can be costly (and is not always straight forward) and insurance companies will usually not insure the horse for treatment of these if he/she is purchased with sarcoids already present.

If you are concerned your horse or pony has a sarcoid or a suspicious lump call us for advice. If you have a good quality digital camera/phone, photos can also be e- mailed to us for one of the vets to look at. If you e-mail us a photo, please also include a little information regarding location, size and appearance of the lump and your up-to-date contact details so we can contact you.

To view/download a copy of this information in PDF format, please click here.

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