Equine Viral Papillomata:
It is quite common for horse owners to check their young horses and find that one has a nose covered in small grayish or skin-colored bumps. These bumps are viral papillomata or warts. They're often called baby warts, because they most frequently affect young horses. Older horses rarely get warts, and a horse doesn’t usually have more than one bout with them. They look unsightly, but they aren't really anything to be overly worried about. They are an inconvenience if you want your horse to be well turned out for the show ring, but beyond that, there is rarely a reason not to let them run their course. Many people regard them as the 'teenage acne' of the horse world. Annoying for most, painful for a few, but destined to disappear and not return as the horse matures.
Older horses may be affected by something called pinnal acanthosis. These warts in the ears may never go away, and may be removed by surgery if they are a problem.
Papillomata, Baby Warts, Warts, Milk Warts, Grass Warts
Warts are caused by the equine papilloma virus. They are very similar to the warts humans can have, although you don't have to worry about the virus transferring from your horse to you, or from you to your horse. Baby warts may be transmitted from the mare to the foal as the foal nurses. Young horses often catch them from each other, or they may pick up the virus from buckets, fences or any other place a curious young horse may stick its nose or brush against. They are most likely to affect horses less than a year and a half old.
Warts appear on a horse as small, grayish, irregular bumps. Most commonly seen on the nostrils and muzzle, they can also appear on any hairless or thinly haired area on the body, such as eyelids, or front legs. They can appear quite suddenly. There may be a few, or the whole area can appear almost encrusted with cauliflower-like bumps. If there is more than one young horse in a herd, they will probably have them at the same time. If there are many warts in an area of the body that is very mobile, like the lips and nose, the skin may crack and bleed and there is a possibility of secondary infection. It's not unusual for a wart to 'break off' and bleed as well.
Warts are common. Most horse owners know what they are, and don't need a veterinarian to diagnose them. If there is any question, a veterinarian can take a biopsy and confirm that they are just warts and not sarcoids or other skin problems. If the skin or the warts are cracking and bleeding, the veterinarian may prescribe a topical solution with an antibiotic to sooth the area and prevent infection.
For young horses, treatment is not usually necessary as the warts will go away spontaneously within a few months as the horse develops its own resistance against the virus. The warts disappearas mysteriously as they come. Warts on older horses may not go away on their own. If for some reason, they are a problem, it is possible for your vet to administer a vaccine. It is also possible to remove them with surgery, laser surgery, or cryosurgery. This may be a solution if the warts are in a place that causes pain, such as the girth area. Skin irritation caused by warts can be treated with antiseptics and by keeping the area clean.
Other than basic stable hygiene, there's little that can be done to prevent horses from getting warts. If you only keep older horses, you're unlikely to see warts on them and need to be aware that lumps and bumps can be signs of other problems. If one young horse gets them, and you'd like to prevent others from developing them, you can keep the horses separated and use individual buckets, feed bins and other equipment to prevent carrying the virus from horse to horse. But because the virus may be present before you see any presence of actual warts, this may not be entirely effective.