Endotoxemia in Horses

Kaela Schraer, DVM
By Kaela Schraer, DVM on Dec. 13, 2023
Veterinarian looking after horse

In This Article


What Is Endotoxemia in Horses?

Bacteria contain substances called endotoxins, which are released when the bacteria die. In cases of severe inflammation or infection, high numbers of bacteria can release a significant number of endotoxins into an animal’s bloodstream, resulting in endotoxemia. Endotoxemia in horses is a medical emergency and requires immediate veterinary care.

Endotoxins can be extremely harmful and damage surrounding tissues and organs. They also have profoundly damaging effects on blood flow and blood clotting.

Endotoxemia is closely associated with different secondary responses the body may have: systemic inflammatory response syndrome (SIRS) and disseminated intravascular coagulation (DIC).

Symptoms of Endotoxemia in Horses

  • Fever

  • Toxic line (a red line on the gums above the teeth)

  • Lethargy/weakness

  • Lack of appetite

  • Neurologic changes (dullness, tremors, seizures, ataxia)

  • Diarrhea

  • Tachycardia (rapid heart rate)

  • Tachypnea (rapid breathing)

  • Laminitis

Causes of Endotoxemia in Horses

Endotoxins are released into the blood when an infection causes a large amount of tissue and organ damage. This damage causes the barrier between the tissue and the bloodstream to break down, allowing bacteria and their byproducts to enter the blood.

Horses can develop endotoxemia in a variety of ways, including:

  • Colic with severe blood flow disruption to the gastrointestinal tract

  • Pneumonia

  • Retained placenta following birth

  • Failure of passive transfer of antibodies from mare to foal

  • Other causes of severe systemic infections (cellulitis, wounds, etc.)

How Veterinarians Diagnose Endotoxemia in Horses

Diagnosis starts with a thorough history to determine if the horse has had one of the predisposing conditions. Next, the veterinarian will perform a full physical exam to look for symptoms.

Blood work will be performed to check white blood cell counts and electrolytes. A stall-side blood test called a serum amyloid A (SAA) can be a useful tool for determining levels of inflammation quickly and is also useful for determining if a horse is responding to treatment.

Depending on the cause and progression of the disease, imaging such as an ultrasound or radiographs may be useful as well.

Treatment of Endotoxemia in Horses

Endotoxemia is an extremely serious condition with a very poor prognosis. Treatment typically focuses on preventing infection and endotoxemia in the first place or removing the cause once it occurs.

Treatment largely depends on the source of infection. For example, in endotoxemia resulting from colic, the damaged or non-vital intestines must be removed. In postpartum mares, any portions of a retained placenta must be identified and removed.

Additional treatments may include:

  • Antibiotics to combat the underlying infection

  • Non-steroidal anti-inflammatory medications (NSAIDs) to decrease inflammation

  • IV fluids with electrolytes to combat shock and dehydration and to support organ function

Recovery and Management of Endotoxemia in Horses

The prognosis for endotoxemia is very poor and recovery can require a long period of intense treatment. Endotoxemia can cause severe organ damage, especially in the lungs, heart, kidneys, and liver. It can also cause laminitis by damaging the blood flow to the hooves.

Unfortunately, most horses do not survive endotoxemia.

Preventing Endotoxemia in Horses

The best way to treat endotoxemia is to prevent it from occurring in the first place.

  • Colic: Call the veterinarian at first signs of colic to ensure your horse doesn’t progress too far before treatment.

  • Retained placenta: Manage pregnant mares carefully and ensure the placenta has passed within three hours of birth. A veterinarian should examine the placenta and make sure there are no pieces missing.

  • Failure of passive transfer: Ensure foals get up and nurse within the first two hours after birth so they get the colostrum (first milk) from the mare.

  • Wounds/cellulitis: Keep all wounds clean and have any larger wounds, or wounds that appear infected or abnormal, promptly examined by a veterinarian.

Endotoxemia in Horses FAQs

What causes horse toxemia?

Toxemia is caused by severe infections that result in large numbers of bacteria releasing endotoxins into the bloodstream of a horse.

What is endotoxemia in horses with colic?

Endotoxemia occurs during a colic when the blood supply to the bowel is cut off because of a torsion or entrapment. This causes the bowel to die and leak bacteria into the horse’s bloodstream.

What causes a toxic line in horses?

A toxic line is a bright red line on a horse’s gums. It is caused by the changes in blood flow that occur when endotoxins are released into the bloodstream.

How does endotoxemia cause laminitis?

Laminitis occurs secondary to endotoxemia because of the way that the endotoxins affect the blood flow to the hooves and the extreme amount of inflammation they cause.

Featured Image: Ivan-balvan/iStock via Getty Images Plus


Morris, Debra Deem. “Endotoxemia in Horses.” Journal of Veterinary Internal Medicine, vol. 5, no. 3, 1991, pp. 167–181. WileyOnlineLibrary, https://doi.org/10.1111/jvim.1991.5.issue-3.

Saunders, W B, and G Barrie Edwards. “Gastroenterology 1. Colic.” Equine Medicine, Surgery and Reproduction, Second ed., Saunders/Elsevier, 2013, pp. 21–47.


Kaela Schraer, DVM


Kaela Schraer, DVM


Dr. Kaela Schraer graduated from Tufts Cummings School of Veterinary Medicine in 2017 with her doctorate in veterinary medicine. After...

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