Abscesses and Cysts

Image of a white horse's leg with swelling on it.

Cysts and abscesses can both form lumps on a horse’s body. However, they stem from different causes. Infections cause abscesses, which are full of pus that accumulates under the skin. Cysts are typically present from birth or form during a horse’s development. In some cases, a veterinarian will recommend draining or surgery for both cysts and abscesses. If a cyst is not causing your horse pain, your veterinarian might encourage you to leave it alone.

Abscesses

A nail in the hoof, a wound and bacteria are all possible causes of an infection. When your horse has an infection, a lump of damaged white blood cells may form at the infection site. This infected area naturally becomes walled off to isolate the infection. Pressure in this lump usually causes inflammation and pain. You might notice pus, swelling under your horse’s skin, a firm lump, a tender lump, a lump that’s hot to the touch and / or lameness.

If your horse has an abscess, consulting with your veterinarian is critical. Your vet might want to take a pus sample to send to a lab for analysis. Your horse may need antibiotics, treatment with a poultice or other method of draining the abscess. Hoof abscesses may require hoof trimming.

Your horse may feel better immediately after your veterinarian releases pressure in the abscess.

Bone Cysts

The stifle joint is the most common place in a horse’s body for bone cysts to form. This joint, where the femur, tibia and patella meet, is akin to the knee in humans. Less commonly, cysts form in the elbow or in other parts of the horse. Bone cysts are also called subchondral cysts, as they usually form within a joint, underneath the cartilage.

Riders often first notice something is wrong because of intermittent lameness and a shortened stride. About 75 percent of horses diagnosed with bone cysts are under 4 years old. Usually, the cysts form during abnormal development early in a horse’s life, especially if the horse has larger bones or grows faster than the average horse. Poor diet can also contribute to cyst formation, including imbalances between calcium and phosphorus, copper deficiencies or excess zinc.

Uterine Cysts

Older mares who have had several pregnancies and births are the likeliest candidates for uterine cysts. What starts as uterine scar tissue winds up clogging lymphatic drainage channels, causing a fluid backup. Cysts form around this fluid.

Uterine cysts may or may not be serious. A few cysts do not make much difference to a horse’s wellbeing, unless they are very large. If the cysts are too large or numerous, they can form a barrier that blocks semen from entering the uterus. If a mare with major uterine cysts does manage to become pregnant, the cysts can compromise the embryo’s mobility.

In some cases, surgery remedies the uterine cyst problem. If the uterus is healthy, chances are good that the mare can get pregnant again and carry a fetus to term. However, too much scar tissue and adhesions will leave her infertile after surgery.

Keratinized Skin Cysts

Keratinized skin cysts are rare in horses. The two most common types are dermoid cysts and keratomas. Thoroughbreds are the likeliest horses to develop dermoid cysts. These cysts form around hair shafts, usually on the back of the horse’s head or along its spine.

Keratomas most often form in the hoof wall of the horse’s toe, or, more rarely, its heel. Usually caused by a traumatic injury, keratomas can take a while to present themselves. Degradation of bones may eventually cause lameness.

Skin cysts may occur alone or in groups. They are benign. Your veterinarian may want to remove keratinized cysts. Do not do it yourself. Squeezing the pimple-like cysts can release their contents into your horse’s body, causing a serious inflammatory response.

If your horse has any suspicious-looking lumps, is going lame or seems to be in pain, call us today. We will act immediately to optimize your horse’s health.

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Read What Our Clients Say

  • "Kath, thank you so much for being Greyson's vet, your gentle hand, compassion and great skill made all the difference for my buddy."
    --Deirdre Dekking, Portland
  • "Dr. Mertens is a very friendly, knowledgeable equine veterinarian (and a friend to the rest of the farmyard, including the chickens!). Always up to date on the latest in equine health, and even though Mertens Mammals is a small clinic giving you the personable experience, Dr. Mertens also has equipment for more advanced diagnostics and procedures!"
    —Ari Gordon, Boring
  • "I have been a client of Mertens Mammals for 10 years. Kath (Dr. Mertens) is the most kind, thoughtful and caring Vet I have ever had for my animals. I have 3 horses: my Appy "Breeze" who turns 30 this year, my Paint " Rocket " 14 and my other Paint "Fergie " 3 are all under Kath's care. I also had a dog "Cowboy" who I lost to cancer last July. Kath took care of him also. Dr.Mertens came out on Mother's Day about 7 years ago to treat Breeze for a cut above her right eye. After a few weeks of recovery we were happy to not have a huge scar. Kath also spent 2 hours with me 3 years ago when Rocket had a small case of colic. (Thank God). I couldn't ask for a better person to take care of my girls. Kath always calls to check in on the patients. When people ask who I use for my veterinary needs for my horses, I'm always proud to refer them to Mertens Mammals. I am so thankful for an honest and caring Vet. Thank you, Kath!"
    --Michelle Schatz, Portland
  • "I got looking at Sassy’s records and it will be 6 years in July when you first met Sassy—I feel so fortunate that you became her vet and have looked after her all these years. You are such a wonderful and caring doc and I know you always have Sassy’s best interests at heart. I also know I can always rely on you to help me or Sassy when needed. Thanks for all you do for both of us—will keep you posted on Sassy.”"
    —Judy Becker, Eagle Creek
  • "My horse, Pester, would have lost her eye had it not been for the great care and dedication by Mertens Mammals. They are truly there for you any time you need them. I could go on and on. Kath Mertens has been so good to us!"
    --Troy and Wendy Mohr, Estacada
  • "She has always been there for us. She is forever in my thoughts as the best vet. She saved our hours old filly from certain death. She knew exactly what to do in an instant after just seconds in seeing her. We are forever in your debt...thank you!"
    Barbara T.
  • "Thank you Dr Mertens for such a thoughtful and careful job with our sweet Daisy the Donkey this morning! She is well on her way to health again after that abscess!"
    Suzi C.