The lowdown on the common lumps and bumps of horses

Horse Health: Often the best treatment is benign neglect until they get better on their own

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Over their lifetime, horses present with an array of lumps and bumps on various occasions. At times the lump or bump will seemingly appear suddenly from out of nowhere, or it may develop slowly and remain for years without change. The behaviour and clinical picture of the lump/bump will determine whether it needs further investigation and attention, or whether space and time is the best course of action.

Whenever a new mass or swelling occurs acutely on a horse, within hours to days, a hematoma or a seroma is a likely candidate. These swellings are usually linked to trauma from a kick or some type of collision. The tissues are bruised during the injury and hemorrhage or serum leak under the skin to form the mass. Although unsightly and sensitive to touch, these masses are usually of little consequence to the horse as its body heals the damage, reorganizing the tissues and reabsorbing the fluid. This slow process yields the most cosmetic result and requires no further treatment other than patience. It may take up to two months for the swelling to fully resolve.

Bacterial infection

If the hematoma or seroma becomes invaded with bacteria an abscess is a possible complication. If such occurs, medical intervention will hasten its resolve and usually involves drainage and flushing of the abscess. Hematomas, seromas, and abscesses will generally occur on the horse’s upper body rather than the limbs.

Swellings which occur on the limbs may be accompanied by varying degrees of lameness. Fluid swellings along tendon sheaths, “pouchings” of joints, and painful swellings along bony surfaces often necessitate further investigation to determine their cause and thus proper treatment to ensure a successful outcome. Some of these may require simple rest to resolve, whereas others may require extensive medical treatment and a daily regime.


Horses can also get the typical flat-topped skin nodules known as hives whenever they have an allergic reaction. Although hives can occur during any season, they tend to have a higher incidence during the summer months and can present as a singular wheal or as multiples covering large areas of the body. They are sometimes accompanied by itching, scabs, and serous discharge.

Hives develop suddenly and often disappear just as suddenly as they arrive. They tend to be an immediate skin reaction to an allergen, which is a catch-all term referring to numerous inciting causes.

Biting insects are the most common culprit however reactions to drugs, chemical fly sprays and shampoos, vaccines, plants and feedstuffs are all possible allergen agents.

Just like certain people, certain horses have greater sensitivities as well. Discovering the cause can be challenging yet these animals will not find true relief until the causative agent is removed. In severe cases, the reaction can get out of control and may cause respiratory distress and generalized swelling. Careful monitoring of these reactions is very important. Mild allergic reactions usually clear up on their own with time, however immediate veterinary intervention may be necessary if the horse appears distressed or has difficulty breathing.

Protein bumps

Another type of more persistent skin lump is the eosinophilic or nodular collagenolytic granuloma. These persistent lumps, also know as “protein bumps,” are usually non painful firm “bumpy” swellings. They can be found singly or in multiples, varying in size from small to moderate, and are commonly found along the neck, withers, and back of the horse. Although their exact cause is unknown, they are thought to result from trauma or irritation to the underlying connective tissue. Their presentation is often bothersome to the horse owner as they are typically located where tack contacts the body, i.e. under the saddle. However this situation also provides a valuable clue as to their probable cause and therefore it is a useful exercise to consider that the lumps are in response to an irritation and/or small yet repetitive trauma, such as ill-fitting tack.

Is it cancer?

It is not uncommon whenever a lump or mass appears on a horse for an owner to be concerned about cancer. Whilst skin cancers can develop in horses they are generally considered to be uncommon. The three most common types of skin cancer in horses are sarcoids, melanomas and squamous cell carcinomas and their development is generally slow. Veterinary consultation will be able to determine the best course of action for these, as in many situations they are treatable.

Sarcoids vary in appearance ranging from thickened flat hair-less lesions to a warty fibrous-like nodule of considerable size. They can be found anywhere on the body. Treatment is variable, depending on location, type, and size of the tumour with no one treatment considered to be curative. The squamous cell carcinoma is found in association with the mucous membranes near the skin in locations such as eyes, vulva, and penis. Recommendations for treatment are based on their individual specifics. Removal or cryotherapy are the most common treatments, and are best attempted early, when the mass is small.

Melanomas are most commonly found in grey horses and typically appear under the tail and along the perineum or vulva. Generally they are best treated with “benign neglect” meaning — simply left alone. Treatment, if chosen is variable and includes removal, chemotherapy, and trial with a new vaccine. Recommendations are based on individual cases.

The challenge with lumps and bumps on horses is in determining which ones are significant and need further investigation and which ones can be cared for with indifference. Veterinarians are a valuable resource for providing diagnosis and further direction whenever the nature and proper treatment of a lump or bump is in question.

About the author


Carol Shwetz is a veterinarian focusing on equine practice in Millarville, Alberta.



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