It is highly likely that horses inherit the predisposition to sarcoid development. In an ideal world we would avoid breeding from horses known to be predisposed to sarcoids, however that is not practical given that many horses will be lesion free even if they are predisposed.

If you breed from a horse that has had many sarcoids there is a high chance that its offspring will also be predisposed. However there is no test currently available that identifies a predisposition to sarcoid.

Close contact with a horse affected by sarcoids increases the risk of sarcoid development. Foals born to mares affected with sarcoid are likely to carry a genetic predisposition to sarcoid formation in the future.

The groin/udder region is commonly affected and so mares may have various forms of sarcoid that will come into direct contact with the foal while it feeds. Foals of mares with sarcoid are therefore at greater risk of developing sarcoid both because of their close relationship and because of the genetic link.

Mares with sarcoids that are used for breeding should be carefully examined and treated to ensure that the sarcoids are as small as possible when they foal. Bleeding, ulcerated sarcoids are the most risk to the foal particularly if the flies are not controlled.

Any drug or toxin absorbed into the body (by mouth or through the skin) when pregnant will pose a risk to the unborn foal. This is widely accepted in humans. The treatments for sarcoids often involve chemicals designed to kill dividing cells. The unborn foal is also in the process of dividing many cells and so is at greater risk than an adult of having side effects.

Surgical treatments that require sedation or anaesthesia will also carry risk to the unborn foal. Your vet will provide guidance on the best approach.

Treatment with chemical drugs of any form should probably be avoided in the first 120 days of pregnancy. Treatment of sarcoids before mating is preferable if at all possible.

Sarcoids appear to multiply in number over the summer and then grow bigger over the winter. This means that the first time you notice them is at the end of the winter. It can be hard to check your horse thoroughly over winter when its dark much of the time but you should be checking your horses full body in daylight at least weekly.

Owners should perform a thorough examination of their horse in the springtime prior to summer turnout and seek advise promptly for any new lesions.

A horse that has any sarcoids is liable to them and will remain so for life. This means that being vigilant to any new skin lesions developing. Early treatment of sarcoids, careful wound management and stringent fly control reduces the risk of further sarcoids developing. There are a tiny number of horses that appear to self-cure at an early age. These horses may be sarcoid free for the rest of their lives however they are a very small minority.

Some individual sarcoids can resolve on their own even when others on the same horse do not. There is no predictable time scale for this to occur – some cases will resolve totally within days after having been affected for years.

Horses treated for the disease (no matter how effective the treatment is) are always likely to develop new sarcoids at some point in the future.

There have been reports of new sarcoids developing in horses that are in contact with cattle. This has been linked to sarcoids caused by Bovine Papilloma Virus (BPV-1) which may be transmitted by flies.

The majority of horses developing sarcoids have no history of cattle contact at all so there is no value in avoiding cattle contact. Understanding if you horse is susceptible to sarcoids and taking sensible fly control measures is far more important than avoiding contact with cattle.

Sarcoids commonly develop and multiply at sites where flies feed. It therefore seems likely that they are involved in the disease. Flies prefer to feed on open and verrucose sarcoids. We advise strict fly control and careful and prompt wound management to reduce the risks that flies may pose to horses predisposed to sarcoids.

It is unlikely that a virus is the sole cause of sarcoids. Virus-like genetic material has been found in a high proportion of sarcoids but no virus particle has yet been identified or isolated. In viral causes of skin lesions we tend to see an immune response to the virus just before they self cure (this is seen in equine viral papilloma)

Horses with sarcoids don’t appear to mount any sort immune response to the virus thought to be involved which means that a vaccine for this virus would not protect against sarcoids.