Intestinal Bacterial Infections in Horses

Endotoxemia in Horses

The presence of endotoxins in the blood is referred to as endotoxemia. These toxins are generally due to the presence of certain types of bacteria in the horse's gut that have breached the gut wall and entered the blood stream. If not treated promptly, endotoxemia can lead to shock, laminitis, and death. This condition is seen both in adult horses and in newborn foals.


As previously stated, endotoxemia may lead to shock, more specifically endotoxic shock. This is an extremely dangerous condition that leads to rapid deterioration and will cause death if treatment is not instituted immediately. Symptoms of this condition include:

  • Depression
  • Lethargy
  • Dehydration
  • Anorexia
  • Acute diarrhea
  • A rise in pulse rate (i.e., in excess of 80 beats per minute)
  • Dark purple mucous membranes
  • Colic-like symptoms (e.g., abdominal pain, bloating, gas)
  • Fever followed by abnormally low temperature

As the disease progresses the horse may develop laminitis, a painful and debilitating hoof condition that causes the hoof wall and the bone inside the hoof to separate.


The cause of endotoxemia is the toxin called lipopolysaccharide (LPS), which is present in the cell walls of gram-negative bacteria. Some types of gram-negative bacteria are naturally in the gut flora and don’t cause any harm unless the horse is sick for some other reason and these bacteria begin to excessively proliferate and then breach the intestinal wall, thus entering the bloodstream. When these bacteria die, their cell walls rupture, releasing the LPS into the bloodstream and causing endotoxemia. E. coli, Salmonella, and Enterobacter are common Gram-negative bacteria that cause endotoxemia.

Some precluding conditions that can lead to the development of endotoxemia include:

  • Damage to the mucous barrier in the intestines
  • Inflammation of the small intestine
  • Twisted gut
  • Colitis (a severe intestinal condition brought on by stress)
  • Acute metritis (severe inflammation of the uterus due to infection, usually from a retained placenta)
  • Infection of the umbilicus in foals
  • Insufficient ingestion of colostrum in foals


Horses develop endotoxemia secondary to another serious disease and these animals are already very sick and likely already in the hospital. Endotoxemia is diagnosed by clinical signs and sometimes by bacterial culture of the horse’s blood.


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