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Diagnosing and Assessing Swellings in Horses

Diagnosing and Assessing Swellings in Horses

by Robert N. Oglesby, DVM

Do you have a swelling under the skin and you are unsure what it is? This is the place to start.



Swellings are a very common problem in horses with many causes, as a result we have a number of different articles on this subject. This article is designed to explain the causes of swelling, help differentiate the various types, and then direct you to more specific topics on the specific swelling. Note that bumps, lumps, and tumors of the skin are discussed elsewhere. Some swellings are obviously part of the skin but if you are uncertain try moving the skin around the swelling. Does the swelling move with the skin or does the skin move over the top of it? If it moves with the skin most likely it is associated intimately with the skin and discussed in the article on skin bumps and tumors, ...for more information.

In this article tumors and generalized swellings of the tissues under the skin are discussed. The differences between non-inflammatory and inflammatory swellings are outlined and the common swellings that occur in horses are identified by their characteristics and location. Links to more specific articles on further diagnostics, treatment, and prognosis are provided.


Article Summary

  • By knowing whether your swelling is inflammatory and/or edematous you can greatly reduce the number of possible causes.
  • Once the cause is known more effective treatment can be instituted.
  • There are a number of common swellings that can be diagnosed by their location and characteristics. Images and descriptions of the common swellings and tumors of horses are provided.


Is the swelling caused by inflammation?

The common swellings of the horse are often best understood by separating them into inflammatory and noninflammatory processes. So what is inflammation? It is the body's response to physical insults like trauma, infection, allergies, and autoimmune diseases. Inflammation results in serum (the liquid part of the blood) leaking out of the blood vessels and collecting in and around the tissues, which is why swelling is associated with inflammation. Inflammation is recognized by redness, heat, swelling, and pain. It is difficult to detect the redness of inflammation with the highly pigmented skin of most horses so swelling, heat, and pain are the hallmarks in horses.

Not all swellings are inflammatory. Noninflammatory swellings are no different in temperature than the surrounding non-swollen areas and are not painful. They are often chronic in nature and persist or recur under certain conditions. Very mild inflammation or early in the inflammatory disease process there may be minimal heat and pain so frequent reassessment is a good practice it uncertainty about the nature of the swelling exists.

The presence or absence of heat and pain are detected by careful exploration of the swelling. This is best done in a quiet and relaxed atmosphere. Horses often react when you touch and squeeze them even when not painful so first carefully evaluate for reaction by palpating non-effected similar areas. This gives you several benefits:

  • You can observe the horses normal reaction to such an exam.
  • You can observe the normal temperature of the area.
  • It allows the horse to get use to this type examination.

After careful and thorough exploration you should be able to decide which description best fits your horse:

Is this swelling associated with edema?

After deciding whether your swelling is caused by inflammation the next step is to determine is it caused by edema. So what is edema. Our body contains a fair amount of fluid, outside of blood vessels, lymphatic vessels and the cells. This extracellular fluid bathes the cells and aids in the movement of nutrients and waste products. It also has important inflammatory components. When excess fluid accumulates between the cells and tissues it causes swelling. Edema is recognized clinically because it pits on firm pressure and then is slow to refill, taking 5 to 30 seconds.

There are many causes of edema, some inflammatory and some not. However by knowing whether or not the tissues are inflamed and by knowing whether it is edematous or not greatly decreases the number of possible causes of the swelling.

Cool, Nonpainful Swellings




Generalized Swelling In Lower Legs or Ventral Midline
That Is Edematous

The swelling is the same temperature has non-swollen surrounding tissues and is does not show evidence of being painful.

This is passive edema where fluid has become congested in the tissues and not associated with inflammation.

  • Poor circulation from venous or lymphatic congestion.
  • Tissues have lost their normal elasticity and now fill with fluid especially when not exercised
  • Inflammation dorsal (above) the swelling and gravity has pulled down the fluid into non-inflamed tissues.
  • Low amount of proteins in the blood decreased the osmotic pressure that helps keep fluid in the vessels.
  • bilaterally generalized lower limb swelling, most often associated with stalling, is very common and most likely stocking up.
  • Major organ failure (often there is other signs of disease with these causes):
    • congestive heart disease: depression, exercise intolerance, multiple areas of swelling
    • kidney failure.
    • liver disease.

Swelling Is Associated with a Joint or Tendon
but is Not Edematous

A soft to firm fluid filled, well defined swelling, associated with a joint capsule or tendon sheath. Not painful on palpation there is no lameness associated with the swelling. Though it pits on pressure, it springs right back when released. In chronic conditions often both legs are effected (bilaterally symmetrical).

Mild inflammation or loss of elasticity of a synovial sheath like a joint capsule, tendon sheath, or bursa. If acute and unilateral may represent blunt trauma or miss-step. Trauma from repetitive over-stretching during work outs.

  • Hocks: Bog Spavin and/or Throughpin
  • Calcaneal Bursitis: Capped Hock
  • Fetlocks and Flexor Tendon Sheath: Windpuffs

For more on localization of these conditions and links to these diagnoses see images below.

It feels like a tumor or cyst not associated with a joint or tendon. Well defined swellings that are soft to firm but don't pit or fell bone hard.

Many normal and abnormal structures might fit this description so location and history important to define cause.

For more on localization of these conditions and links to these diagnoses see images below.

Hard Swellings on the Bone
A hard bump ow swelling attached to a bone, it can be anywhere bone lies just under the skin.

Bone responds to growth, stress, or bruising by laying down more calcium.

  • Splints
  • Exposed tips of pelvic bones or dorsal spinous processes of very thin horses
  • Blunt trauma to the bone: cannon, inner upper legs
  • The front of the coronet is enlarged: extensor process enlargement
  • Growth plate enlargement at the top of the knees, top of the hocks, or rarely top of the fetlocks of rapidly growing foals....for more information
  • Rapidly growing teeth causing enlargements of the lower or upper jaws of growing horses.

For more on localization of these conditions and links to these diagnoses see images below.

Warm, Painful, Swellings

Swelling, heat, and pain including lameness are signs of inflammation and proper treatment relies on accurately assessing the cause of the inflammation. Trauma, infection, allergies, and autoimmune diseases are all diseases that cause inflammation. If the swelling is warm you should take your horses temperature to see if there is a fever, ...for more information.

Fever is an important way we can differentiate infection from trauma. Trauma and irritants don't usually have fever while infection if remarkable enough does. However there are exceptions. First, many autoimmune diseases, where the body's immune system is attacking itself, have fever. If there is a lot of tissue destruction or if the pain is severe, trauma may present with a increase in temperature. Some infections also do not have fever, for instance well encapsulated abscesses may present as a tumor that is warm and painful but not have fever.




Edematous but No Fever
The swelling is associated with heat and pain including lameness if in the legs. No fever is present and the onset was very quick. It will pit with pressure then slowly refills in 5 to 30 seconds when released.

This is active edema that is associated with inflammation from trauma. The inflammation causes fluid and inflammatory mediators to escape from blood vessels into the inflamed tissues.

Even when fever is not present infection should still be considered when the lesions are confined to a small area, the reaction is superficial like on the skin, draining well, worsening over time or multiple areas (like 2 legs) are effected:

  • Blunt trauma or strain
    • bruise or hematoma
    • tendenitis (inflamed tendon)
    • desmitis (inflamed ligament)
    • fracture (broken bone)
  • Reaction to injection (cellulitis):
    • vaccines
    • antibiotics
  • Skin Infection or irritation from something applied to the skin:
    • Infectious, allergic or contact dermatitis: even though the irritation is on the outside of the skin when the rection is remarkable it can cause subcutanous edema to form. With a very severe reaction there may be fever.
    • Grease Heel of Staph folliculits particularly on the legs.
    • fly sprays
    • liniments (particularly when put under a bandage).

For localization to a specific structure try the images below this section.

Edematous and Has Fever
The swelling is associated with heat and pain including lameness if associated with the legs. Because fever is present infection or autoimmune disease is high on the list of suspects. Occasionally noninfectious processes will cause fever particularly if very painful or excited. The swelling will pit with pressure then slowly refills in 5 to 30 seconds when released.

This is active edema that is associated with inflammation secondary to either infection or autoimmune disease. The inflammation causes fluid and inflammatory mediators to escape from blood vessels into the inflamed tissues.

If fever is present consider infection or autoimmune disease, if not present infection should still be considered in focal lesions that are worsening over time. For localization to a specific structure try the images below.

  • Infection (can be either dermatitis or cellulitis (formerly called lymphangitis)
  • Autoimmune diseases like purpura following Strangles vaccination
  • Equine Viral Arteritis
  • Remarkable lameness and hoof is warm and pastern swollen: consider hoof abscess
  • History of recent injection at site of swelling: injection abscess

Legs with a generalized, hot, painful, swelling have a number of specific causes...for more information. For focal swellings see the images below for localization.

Hot, Painful but Not Edematous

Often these will be infection that is encapsulated in a joint capsule, tendon sheath, or walled off abscess. Note that in time the overlying tissues will usually become hot and edematous making diagnosis of the exact structures that are infected difficult. To find the underlying infection may require ultrasound.

  • Strangles
  • Septic Arthritis, with time the overlying tissues may develop edema.
  • Abscess, with time the overlying tissues may develop edema.

For localization to a specific structure try the images below.

Warm, Nonpainful Swellings, Unsure if Inflammatory

If just minimally warmer than the surrounding skin and their is no pain or lameness consider this may be a transient nonspecific warmth and you should review the cool swellings above. If considerably warmer than the surrounding skin you should also consider the possibility you are looking at a early inflammatory problem that may worsen and has not become painful yet or possibly pain is not a prominent feature of the inflammation. An example of such a swelling would be a broken blood vessel that results in a hematoma or if it seems well encapsulated, a noninfectious abscess.

A further important differentiating factor is whether the inflammation is responsive to NSAID's. Irritants and non-infectious reactions are usually moderately to very responsive to their use. When uncertainty exists, particularly if there is pain or fever associated with the swelling, your veterinarian should be consulted. Further diagnostic work up may include ultrasound, tapping if fluid or biopsy if a solid mass.

Swellings by Location

Below are some of the common locations for swellings. Often just knowing the location, texture, and history allows you to diagnose the cause of the swelling but not always and exceptions always exist. See if you can match up your swelling with one of the locations below and decide whether it is inflammatory or not:

Common swellings around the head:


  • A soft well circumscribed cyst may be a nasal arethoma.


  • multiple firm swellings in a young horse on both sides of the head: normal tooth roots of a growing horse
  • singular swelling in an older horse: abscessed tooth root or sinusitis.


  • A soft swelling in a horse may be a fat pad often associated with older Cushings horse.


  • Firm swellings could be either lymph nodes or salivary glands.
  • Generalized fluctuant swelling may be the guttural pouch.


  • Firm well circumscribed swelling on either left or right side just beside the trachea may be the thyroid gland.


  • Submandibular lymph node when accompanied by fever, cough, and nasal discharge consider Strangles.

Common swellings on the body:

YELLOW: Chronic trauma has resulted in the ischium (the bone poking up making the bumps) pulling away from the sacrum, they are referred to as hunter bumps.


  • On the front of the chest is a pocket of edema or large hematoma commonly associated with kick. Also this is a common location for an abscess from pigeon fever.
  • On the ventral midline under the rib cage: a common location for dependent edema from a number of causes.
    • Trauma from a kick
    • Late pregnancy (normal) and extends back to the mammary glands.
    • If the skin is also irritated this may be a reaction to fly bites
    • Reaction to first use of ivermectin or moxidectin and resulting onchocerca death. Rare in horses that have received past doses of these dewormers
    • Congestive heart failure: there will usually be other signs of severe disease.
    • Kidney or Liver disease: there will usually be other signs of severe disease.


  • Umbilical Hernia

Swellings in the upper front limb:

GREEN: in the chronic condition this would be called capped elbow or shoe boil. This has two potential causes the first being a horse with very high action hitting himself here. Also some horses which lie down a lot might get chronic irritation here.

RED: Swelling here is associated with the carpal canal sheath.

BLUE: A fairly common swelling is a well circumscribed firm fluid filled swelling which represents a herniated radiocarpal joint capsule. Usually not associated with lameness.


  • In adult if acute this would be the appearance of generalized swelling in the front of the knee. If chronic this might be a hygroma. In both cases ...for more information.
  • In foal acute onset associated with buckling of the fetlocks might represent extensor tendon rupture. It can occur bilaterally and is not as serious as it sounds.

Common swellings on the rear limb:

MAGENTA: A fluid filled non-pitting swelling on the front or inside of the leg would represent a distension of the stifle or femorpatellar joint. These would usually be associated with lameness, ...for more information

DARK BLUE: Fluid filled non-pitting swelling on front of the hock is called a bog spavin (distended medial sheath of the tarsocrural jt).


  • When accompanied by the Dark Blue swelling and just on the outside it is the distended lateral sheath of the tarsocrural jt).
  • When accompanied by a similar swelling on the inside of the leg it is called a throughpin and is the distended tarsal sheath of the flexor tendons (tendosynovitis).

RED: Hard chronic swelling: bone spavin (osteoarthritis of the distal tarsal joints).

YELLOW: Usually caused by distension of the calcaneal bursa (bursitis) it may or may not be associated with lameness. When it is radiographs, ultrasound and possibly tapping the bursa should yield a diagnosis.

GREEN: Swellings here are referred to as curb and can have a number of different causes, ...for more information.

Swellings in the lower limbs:

GENERALIZED LOWER LIMB SWELLINGS: Cool swellings in the lower legs, particularly the rear ones, when stalled. Usually bilateral, the swelling starts in the pasterns but often can run up into the cannons. Though the ankles may be involved, the swellings are not specifically associated with the joints or tendon sheaths. Soft to firm to the touch it will pit with pressure then slowly refills when released. This is passive edema (serum that is filling the tissue) and called stocking up...for more information.

DARK GREEN: Old firm swellings not associated with lameness represent a healed flexor tendinitis. When acute and painful proper treatment is important to minimize damage and promote healing, ...for more information

YELLOW: A hard swelling associated with the splint bone. Splints can occur anywhere along the splint bone but often high up on the splint...for more information.

LIGHT GREEN: Distended flexor tendon sheath, often called windpuffs when chronic and not associated with lameness.

BLUE: Distended volar pouches of the fetlock joints, often called windpuffs when chronic and not associated with lameness.

MAGENTA: Generalized swelling of the fetlock joint.

RED: Locations for ring bone but the lower one could also be an enlarged extensor process of the coffin bone and not always associated with lameness.

LIGHT BLUE: The lateral cartilages are normally palpable along their upper edge but can be enlarged and calcified and referred to as sidebone.

Note: this article is meant to help you diagnose the problem with your horse and is not meant to take the place of veterinary care. If your horse is distressed you should consult your veterinarian.

For More Information:

  • On this and other fine internet sites:

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  • From the Nat. Library of Medicine:

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