Horses often get banged and bruised by running into things, being kicked by another horse, falling down when running and bucking, etc. It's not unusual to suddenly discover your horse has a large, soft lump on some part of his body. The most common areas are the hindquarters, chest, or along the ribs. The skin might not be damaged, but the injured tissues underneath can bleed or ooze serum, creating a large "balloon" under the skin. The damaged blood vessels usually don't stop bleeding until there is enough pressure from the fluid accumulation to halt the bleeding and allow the blood to clot.

Hematomas (swollen, bruised areas) generally are unsightly, but aren't tremendous health problems. However, without proper diagnosis--and occasionally veterinary treatment--they can become long-term health problems.
Claude Ragle, DVM, Dipl. ACVS, Dipl. ABVP, associate professor of surgery at Washington State University (WSU), says it's hard to make generalized statements about how to treat hematomas, or bruises, because there are so many variations in location and seriousness.

When a horse suffers a hematoma, it's always wise to have a veterinarian look at it. "You want to be sure of what you are dealing with, and how best to manage it," says Ragle. "Some things that look very innocuous can actually be very serious, while others that look horrible may not be a problem. Your veterinarian can sort these out."

Most of the time hematomas are best left alone to resorb. Whether or not the area should be drained by a veterinarian depends on how big it is, how long it's been there, and whether it is interfering with the horse's ability to move.

"It also depends on the size of the blood vessel that is damaged and bleeding," he says. "If a horse has major disruption of deeper tissues (such as getting a leg hung up in something), there may also be torn muscles as well as bruising. Horses can get this kind of damage on the inside of their hind legs, or tear some of the large muscles of the hindquarters. They may have a big hematoma, and this is what you see, not realizing how much damage is underneath it. Stallions can get kicked in the scrotum during breeding and will present as a hematoma, but even more serious is the ruptured testicle beneath it."

There's a wide variety of things you might see. A component of the injury is hemorrhage and swelling under the skin--but how you manage each of these will be a little different, he points out.

"A rule of thumb when treating a closed-space subcutaneous hemorrhage is to not drain the hematoma until the damaged vessels have sealed, because if you open it up, it may bleed more," explains Ragle. "In the beginning, the pressure within the skin is all that is keeping the vessels from continuing to bleed. Veins have lower blood pressure than arteries; blood pressure is an important factor in determining hematoma size.

"If there's a vessel you can identify and your vet can ligate (tie off), that can be a direct approach to treatment," he says. "But often, especially with typical hematomas, a horse gets injured on the hip or breast and identifying a specific vessel is impractical. If you open a hematoma prematurely and it starts bleeding again, you have a bigger problem. Sometimes we choose to operate early if the hematoma continues to expand and is not being confined to a limited area. We may have to isolate it. But if it's reached a static state (and many veterinarians use two weeks as a general time frame for when a hematoma is 'mature,' i.e., the bleeding vessels have sealed), it's a matter of monitoring the hematoma to determine when and if to intervene."

Ragle says there are two basic approaches to treating mature hematomas. "The controversy is whether you should open or drain them, or let them resolve on their own," he explains. "Most of them, given enough time, will start to resolve. It takes weeks to months, however, and in some cases a pocket of serum may remain more than a year. My opinion is that most hematomas should not be invaded before two weeks because it takes that long for the vessel to clot and stabilize, with less risk of hemorrhage starting again if you drain it."

Ragle explains that most of these are sterile swellings, so there is very little pain or inflammation. Over time, the clot will begin to resolve, and the horse ends up with a serum pocket of straw-colored fluid. If you drain that with a sterile needle, he says, often it will reform because it has developed a subcutaneous pocket where the skin is no longer attached to the underlying tissue, and that fills again with serum.

If you try to drain it multiple times with a needle, there is risk for introducing bacteria, Ragle notes. Blood and serum within the pouch is a perfect medium for bacterial growth, creating inflammation and an abscess rather than a sterile hematoma.

"Sometimes a veterinarian will make an incision at the lower portion of the swelling to allow drainage and let it heal from the inside out through granulation and contraction," says Ragle. A certain amount of inflammation is required for that to happen.

Ragle says owners and veterinarians have to make a decision on which is worse for the horse--having a bag of fluid that persists for a year or more, or opening it to drain and risking infection. "Usually it boils down to size. If it has to be lanced to drain, keeping the opened-up area clean can be a challenge, and it may need to be continually flushed until it heals properly from the inside out. The veterinarian may insert a plastic drain that will allow the wound to drain or be flushed as it heals.

"I usually do not open or drain these unless the swelling is large enough to cause some sort of mechanical problem (impairment of movement) for the horse, or is located where there's risk of injury from tack or surroundings," says Ragle. "If by the time I've given it two weeks it's not getting worse and it is tennis ball size or smaller, in a quiet location, it's best to leave it alone."

Ragle says that veterinarians have tried many things to help hematomas resolve quicker, such as draining the swelling and injecting it with an antibiotic and steroid, or adding a small amount of atropine to help it resolve. "Occasionally that works, but often it does not," says Ragle. "Getting the skin to re-attach after it's been separated for a period of time is the challenge. If you drain the blood or serum (so the skin can heal back together) off too soon, while subcutaneous surfaces of the skin are still raw, you may end up with continued hemorrhage. But if you wait until everything is mature, then the surfaces of the hematoma pocket have sealed and it's not as easy for them to stick back together. That's the 'Catch-22,' finding that perfect period of time where it's not going to fill up with fluid again, yet can still grow back together without having the inflammatory reaction caused by open incision drainage."

If an owner actually sees the injury occur, he/she can control the bleeding (and keep the swelling smaller) by applying direct pressure and ice--if it's an area where you can do it and the horse will tolerate it, says Ragle. You want to keep the blood pressure down so the damaged vessels won't bleed profusely into the tissues, so you use pressure and ice. You also don't want to get the horse excited, with his blood pressure elevated, or this can defeat your purpose.

"If you can keep the horse quiet and put an ice compress on the swelling, at least initially, this can help a lot," he says. "Even a little direct pressure for five to 10 minutes can help halt the bleeding and keep the swelling from expanding. The swelling grows because it keeps bleeding--until pressure inside the hematoma itself equals the blood pressure coming into it from the vessels and halts the flow. If it's a small vessel and happens in an area that won't get huge (areas where the skin is tight are less prone to developing pocket-type hematomas), this is what determines what size it will be. If you can catch it early and put direct pressure on it, you may be able to hold it long enough that it clots. The swelling will be smaller than it would be if left on its own. It's worth trying, although most times the horse is discovered hours after it happened and the swelling is already huge."

Debra Sellon, DVM, PhD, associate professor of equine medicine at WSU, says that a pressure bandage or wrap might be used, but often the bruise is in a place where it is hard to apply pressure except by hand.

"Icing it or cold water hosing to stop the bleeding can be very helpful," she recommends. "The pressure and cold applied during the first 24 hours can make a big difference in how much it swells and how long it will take for the fluid to resorb."

Cold should only be applied for about 20 minutes at a time, however, giving the tissues about an hour between sessions. Prolonged cold can be detrimental to the tiny muscles of the blood vessels.

Cold therapy should be continued intermittently for as long as the area feels warm and soft, Sellon says. "Later, after the hematoma has stabilized, warm packs can help increase the circulation and speed healing," she explains. At that later stage, the area under the skin will feel more like gel than fluid. Warmth and massage can help the tissues resorb this gel-like debris and reduce its conversion into fibrous scar tissue.

Ragle says, "When I examine a hematoma or talk to a client, I determine if it's over a joint or crucial structure. Obviously, it's worse if it's in an area where there is a lot of bending or motion. I figure out how deep the damage is. This may require radiographs or ultrasound. You need to know if it's just a subcutaneous skin vessel that's bleeding, or if there is trauma to deeper tissues. Is the stifle joint involved, or bones or muscles? Once you rule out involvement of any other structures, you can allow it to clot. If you open it up too soon, you might not be able to get the bleeding to stop as well as it has."

Ragle recommends limiting exercise until the hematoma is healing. "I tell the owner to keep in mind that even though you want to keep the horse confined, you also have to keep his mind quiet," he says. "Sometimes the best place for him is in a 30-acre field with a buddy, so he's not fretting. If he's pacing the walls in a stall, this is not accomplishing your goal. You need to do whatever works best for that individual to keep him calm and limit his movement. He has to be calm while you are limiting the movement, because if he is unhappy--if all his buddies are turned out and he's used to being out, and he's jumping up and down in a stall--this can make the problem worse."

A Serious Mimic

You always want to be sure of what you are dealing with. Ragle says there is a type of vascular tumor that looks like a hematoma, called a hemangiosarcoma (cancer of the vessels), which seems to occur more frequently in the Northwest than in other regions. "We've seen more of these here at Washington State than I've seen in other places," says Ragle. "Veterinarians at WSU reported a case series that had 35 cases."

Sellon says these can look just like a hematoma because they are tumors of the cells that line the blood vessels. "They can grow in lots of places, including under the skin or in the muscles," she says. "When one of these is in a muscle, you might mistake it for a hematoma. Luckily this problem is rare, but your veterinarian would have to get a biopsy sample to diagnose it."

Ragle says owners often first think the tumor is a hematoma, but they don't respond normally to treatment. "This is why it's good to have a veterinarian examine the swelling," says Ragle, who added that these tumors can be a challenge.

"We don't have an easy test for (diagnosing these tumors)," says Ragle. "But we do know, once we've examined a hematoma, that it should be getting better by the next recheck, and if it isn't--or the horse has another bleed with no excuse for it--we realize something's not right and additional diagnostics are needed."

Sellon describes this as an aggressive type of cancer. "Most horses with it eventually die," she says. "If the horse is having problems functioning (difficulty eating, drinking, or moving around), or the swelling continues to get bigger, or the horse is getting hematomas from minor trauma, these are warning signs," she says.

Another condition a veterinarian will consider when examining a hematoma is hereditary equine regional dermal asthenia (HERDA), also known as hyperelastosis cutis. This is a condition where the skin is very loosely attached to underlying tissues due to defects in collagen synthesis, and the skin is easily traumatized. The problem is hereditary in certain lines of Quarter Horses, says Ragle (For more information, see

Sellon says that if a young horse gets hematomas repeatedly, the cause might be an inherited blood clotting problem, similar to hemophilia in humans. "A bruise under the skin would tend to keep bleeding--a sign of a clotting problem," she says. "Usually we see this in younger horses. But any horse might have trouble if it eats rat poison, which could make the blood fail to clot."

A lump on your horse should always be examined. It could be an abscess rather than a hematoma. In that instance, the swelling will be filled with thicker, putrid fluid or pus. The color of this material might be yellow, white, or reddish, depending on the type of bacteria involved.


Sometimes there is scar tissue left in the area of the healed hematoma, or a little pouch of enlargement that remains for some time. The skin and the tissues beneath it have been disrupted, and sometimes do not grow back together normally.

Occasionally after the swelling goes down and the area has healed, that patch of skin sweats more readily than normal skin. "The sweat glands on a horse are a bit different than those of other species," says Ragle. "It's hard to predict how long some of these abnormalities will persist. Most tissues continue to heal and remodel over time, but it may take years."

The mechanics of hematoma injuries have not been studied or reported in a long-term follow-up; there is not much published data on what happens. There is also not much basic scientific study about hematoma formation and maturation, he says. This is primarily due to their low impact on a horse's performance.

"Mature hematomas have some similarities with a condition we call acquired bursitis (hygroma), such as when a horse gets a capped hock, capped elbow, or capped knee," says Ragle. "Those areas fill with fluid, creating a hygroma. These may start out as a hemorrhage, then end up as serum; you end up with the same subcutaneous pocket of fluid.

"There is no bursa normally at these sites, but once it fills with fluid and the skin edges are separated for a long time, they stay apart," he explains. "Some treatments for persistent hematoma are the same as what we do for these. The acquired bursitis usually has repetitive trauma at its origin and all of those are over bony prominences. This differs from a hematoma, which is usually over a large muscle area. The tight overlying skin of bony prominences is probably why the capped hock or knee tend to resolve better with ice and hydrotherapy--you can often get those to go down," he says.

Take-Home Message

Hematomas generally are unsightly, but aren't tremendous health problems. However, without proper diagnosis--and occasionally veterinary treatment--they can become long-term health problems. Also, owners might not be able to tell the difference between a hematoma and a vascular tumor that is much more serious. And if there are structures damaged under the hematoma, only a veterinarian can diagnose the extent of the injuries and recommend proper treatment. As in most injuries to our horses, time is a great healer of hematomas, but only if there is a proper diagnosis of the extent and type of damage, and proper, timely treatment.

About the Author

Heather Smith Thomas

Heather Smith Thomas ranches with her husband near Salmon, Idaho, raising cattle and a few horses. She has a B.A. in English and history from University of Puget Sound (1966). She has raised and trained horses for 50 years, and has been writing freelance articles and books nearly that long, publishing 20 books and more than 9,000 articles for horse and livestock publications. Some of her books include Understanding Equine Hoof Care, The Horse Conformation Handbook, Care and Management of Horses, Storey's Guide to Raising Horses and Storey's Guide to Training Horses. Besides having her own blog,, she writes a biweekly blog at that comes out on Tuesdays.

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