Swollen legs in the horse can arise due to a variety of causes, some of which can be minor, while others can be a sign of more serious illness. Swelling may be present in one leg, only the hind legs, or in all four legs. In general, swelling tends to occur more readily in the hind legs, and has been referred to as “filling” or “stocking up.”1

Obviously, a horse’s legs are in the lower part of the body. Thus, due to gravity, fluid can build up within the tissues. This is known as edema, and can occur from issues such as a cut or scratch, to more serious issues such as cellulitis or lymphangitis.2 

Cellulitis and lymphangitis are among the more serious causes of leg swelling in the horse. Cellulitis is an inflammation of the skin and the soft tissues underneath. Lymphangitis in an inflammation of the deeper tissues and vessels that move lymph through the horse’s body. Both of these conditions are caused by bacterial infections that enter the horse’s skin through open wounds or scratches, and are conditions that merit immediate veterinary care.1

Symptoms of Leg Swelling in the Horse

Symptoms horses may exhibit due to swelling in the legs can include:

• Swollen joints in one or more leg

• Pain in the limbs

• Trauma to the limbs

• Cuts or scratches on the lower legs

• Loss of appetite

• Fever

• Legs are warm to the touch

• Lethargy

• Lameness

As indicated above, sometimes swelling in the leg or legs of a horse can indicate conditions that are not serious. For example, occasionally, swelling can result from inactivity in a horse that is accustomed to a high level of activity. The owner may suddenly notice (as in, overnight) that their horse’s rear legs are puffy and swollen. The legs are not unusually warm, and the horse may move somewhat stiffly but is not truly lame. This sort of swelling or “stocking up” is not serious and typically dissipates as the horse is exercised. This scenario tends to be more common in older horses and can affect all four legs, although it is typically seen in the hind legs.2

If a horse has leg swelling accompanied by lameness, warmth in the leg or an elevated body temperature, this indicates a more serious condition and it is time for veterinary intervention. Swelling in a single leg typically indicates a more serious condition than mild edema due to inactivity. Horses are notorious for developing leg infections due to scratches, cuts or punctures so small that they are difficult to find. In such cases, the leg is likely to be warm in addition to being swollen. This swelling will not go away after activity, and will probably get worse until the wound is cared for and any infection is treated.

A horse with significant swelling in all four legs may be suffering from a systemic illness. This could be indicative of heart trouble, liver or kidney disease, or a bacterial or viral infection. 

Lymphangitis in the Horse

Lymphangitis is a bacterial infection that presents with leg swelling in the horse. Often recurring, this condition can affect any horse of any breed. With lymphangitis, a horse will experience onset of a dramatically swollen leg (usually a hind leg), extreme pain and an elevated temperature. Often, these horses will not eat and will be depressed. Some horses with lymphangitis will tremble, breathe rapidly and sweat. The limb may have "pitting edema" and the horse may make concerted efforts to avoid manipulation of the painful limb(s).3

There is no solid consensus among equine veterinarians and researchers as to why horses are so susceptible to lymphangitis and why the onset can be so aggressive and painful to horses. Some believe that the relatively poor circulation in the horse’s lower legs (which tends to favor edema to start with) allows the proliferation of pathogenic bacteria that would be eradicated in areas of the body with better circulation.2 Thus, even small cuts or simple abrasions to the leg can allow access to bacteria. 

Most often, the bacteria isolated from horses with lymphangitis are Staphylococcus, Streptococcus or E. coli species.2,3 These bacteria reproduce quickly, causing the inflammatory reactions of heat and swelling as the horse’s body attacks the bacteria. The lymphatic system reacts by draining fluid from the leg and filtering it through lymph nodes that attempt to flush out the disease-causing organisms. The lymph nodes become overwhelmed and can become infected themselves. From this point, the symptoms tend to cascade, worsening and causing ever-increasing pain to the horse. The accumulated fluid often seeps through the most damaged areas of the skin and present as a dry, yellow crust. Abscesses occasionally develop under the skin as well.3 

Treatment of Leg Swelling in Horses

Trichlormethiazide is a diuretic and anti-hypertensive agent from the benzothiadiazide class which is used in veterinary medicine in cattle, sheep, goats, pigs and horses. Trichlormetiazide also used in humans in United States as a diuretic and anti-hypertensive substance. Marketed under the brand name Naquasone® as a treatment for udder edema in cows, trichlormethiazide is used to reduce mild swellings, especially in the legs of horses, by causing the body to lose water and sodium chloride by decreasing the reabsorption of these electrolytes in the kidneys.4

In equine veterinary medicine, trichlormetiazide is seldom used alone, but is frequently combined with dexamethasone, which is a potent anti-inflammatory. Because each of these medications work via different mechanisms, trichlormetiazide/dexamethasone formulations typically contain smaller doses of the individual drugs than might be used when administered separately.3

Dexamethasone is a glucocorticoid medication that is available in injectable, oral, and ophthalmic forms. It is long acting, and 30 times more potent than hydrocortisone with no mineralocorticoid activity.4 Contraindications include systemic fungal infections, and caution is advised for use in animals with active bacterial infections, corneal ulcers, hyperadrenocorticism (i.e., Cushing’s disease), diabetes mellitus, osteoporosis, chronic psychotic reactions, predisposition to thrombophlebitis, hypertension, and renal insufficiency.

Dexamethasone has been prescribed to treat a variety of equine conditions, including arthritis, allergic reactions, and heaves. It also provides supportive therapy in a wide variety of cases, such as heat exhaustion, influenza, laminitis, and retained placenta, provided that the primary cause is diagnosed and corrected. It is commonly administered orally (PO), intravenously (IV), or intramuscularly (IM).4 Dexamethasone and other corticosteroids suppress the body’s natural production of hydrocortisone, a hormone with many important regulatory functions within the body.

Dexamethasone is typically used in the management of various rheumatic, dermatologic, allergic and other diseases known to be responsive to anti-inflammatory corticosteroids. 

NOTE: The Association of Racing Commissioners International Uniform Classification Guidelines for Foreign Substances has designated Dexamethasone a CLASS 4 DRUG.

Recommended dosages of Trichlormethiazide + Dexamethasone for the treatment of leg swelling in horses is as follows (adapted from Equimed.com):

Where to buy Trichlormethiazide + Dexamethasone 

Trichlormethiazide + Dexamethasone is available in the U.S. through veterinary custom compounding companies. TRICHLORMETHIAZIDE 200 MG/10 ML / DEXAMETHASONE 5 MG/10 ML by NexGen Pharmaceuticals is excellent for the treatment of leg swelling in horses due to acute or chronic conditions.

Please consult your veterinarian prior to beginning any treatment regimen.

FOR RX ONLY: A valid prescription from a licensed veterinarian is required for dispensing this medication.

1Mustefa, K. A Review on Equine Lameness. Int. J. Adv. Res. Biol. Sci. (2019).6(10):101-109.

2Tokateloff N, Carmalt J, Manning S. Trauma resulting in hemarthrosis and long medial collateral ligament desmitis of the tarsocrural joint in a horse. Can Vet J. 2011;52(5):519-523.

3Ameni, G. Preliminary trial on the reproducibility of epizootic lymphangitis through experimental infection of two horses. In: The Veterinary Journal, Volume 172, Issue 3, November 2006, Pages 553-555.

4Plumb’s Veterinary Drugs.