Lumps and Bumps On Your Horse By Megan Williams, DVM Horses, like kids on a playground, seem to have a continuous array of lumps and bumps on them at various times and in various places. It’s a rare horse that you don’t find some sort of lump when running your hand over them. Quite often, these lumps are benign or have been there for years without change and are really nothing to be concerned about. That said, there are times that a horse can develop a mass that can have severe consequences for the health of the animal. The problem sometimes lays in the ability to determine when that “lump” is significant and needs to be investigated or when it can be quietly ignored. Whenever a new mass is found on a horse there is reason for concern as there are a number of possibilities for a lump on your horse that shows up seemingly overnight.

 If your horse develops a single lump of any kind acutely (within hours to days) there are a number of possible causes. A hematoma or seroma is the result of blood or serum “leaking” under the skin to form a mass. These are unsightly and often the horse will be tender to palpation of the region. By themselves these masses are of little concern and the body will work its magic and resorb the fluid with us doing little to no work. However, if even a small amount of bacteria enters the seroma or hematoma, an abscess will quickly form as seromas and hematomas are rich in nutrients for bacteria to multiply. Once an abscess forms, it is far more important that the mass be investigated and treated, especially if an outcome with minimal scarring is desired.


 Lumps found on the lower limbs can have soft tissue implications and may also show up along with a new lameness. There are many tendons and tendon sheaths that will change in shape when excessive strain is placed on them, causing them to “bow” and result in a lump on the back of a horse’s leg. Joints themselves can have small out-pouching in places you may not have normally considered and should be treated with extreme care.


 What about the horse that comes in from the field and is covered in lumps and bumps from nose to tail? Immune reactions such as allergies are quite common in the horse and can happen very quickly. One of the most common situations where a horse develops “hives” all over its body is during a reaction to fly bites often Cullicoides, or gnats. Keeping the horse stalled when flies are out, providing fans, and providing a fly sheet can all help to ameliorate the skin’s reaction. Unfortunately, this may not always be the case and horses, like humans, can have a wide array of allergies be it a contact allergy to a type of feed or bedding, or simply to the latest pollen that is floating through the Florida breeze. These animals will not find relief until the causative agent is removed or treatment is started. In severe cases, the reaction can get out of control and may cause the horse to experience difficulty breathing or moving if their legs swell too much. Careful monitoring is very important.

Often, when a new lump or mass is seen on a horse, people are concerned about cancer. Although certain types of neoplasia (cancer) can develop within a few weeks and grow quickly, these are rare in the horse. Many horses, especially older grey horses, develop benign melanomas. These show up most often under the tail and along the perineum or vulva. Other common places to find them are along the neck, behind the jaw, or under the ear. As a benign tumour, these are often best treated with “benign neglect” meaning that we just leave them alone. If the masses continue to grow and become a functional problem, they can be removed or treated with chemotherapeutic agents.


No matter what the cause of the random lump found on a horse, having them looked at by your veterinarian will help provide direction for how to treat it and deal with any possible similar lumps and bumps that may arise in the future.