Common Causes of Sudden Death in Horses

Man working in a horse stable

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When an apparently healthy horse suddenly dies for no obvious reason, it can leave you feeling confused as well as bereaved. Although a rare occurrence, this could happen to an otherwise healthy adult horse. Here are a few of the more common reasons why this could happen.

  • 01 of 05

    Ruptured Aorta

    lamazeon hickstead

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    The aorta is the large main artery that comes directly from the heart and distributes blood to the rest of the body. In some animals (including humans), a part of the wall of the aorta, which is typically very muscular and rubbery, is thin and weak. This weakened area in the blood vessel is called an aneurysm. A ruptured aorta occurs when this area of weakness bursts. Since the aorta is a major blood vessel, once ruptured, the horse quickly hemorrhages. There is no treatment for this and the horse dies almost immediately. Unfortunately, there is no way to examine a horse and determine if he has an aortic aneurysm.

  • 02 of 05


    Red oak leaves in autumn

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    A horse can die unexpectedly and quite rapidly after ingesting a toxin. Toxins in the environment can include various weeds in the pasture and tree leaves such as bracken fern, red oak, wilted cherry tree leaves and others. Botulism is caused by harmful bacteria that may be in fodder such as silage, or water. Some feed meant for other livestock, such as cattle and chicken, may be deadly to horses because it contains drugs called ionophores. Ionophores are lethal in small doses to horses and cause rapid death.

  • 03 of 05

    Drug Reactions

    Horse receiving vaccination.

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    Allergic reactions to a drug given to a horse can be rapid and difficult to treat. If treatment starts very soon after a reaction is noticed, there may be a good chance for recovery. Despite this, a severe reaction can lead to death very quickly due to anaphylactic shock. Fortunately, this type of extreme reaction is rarely seen in horses on the farm.

  • 04 of 05

    Gastrointestinal Ruptures

    Horses And Donkey On Grassy Field Seen Through Fence

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    Distention and rupture in your horse’s stomach or intestines can cause acute death. The first indication of a severe gastrointestinal problem is colic symptoms. Dehydration and impaction, severe parasite load, a twisting or telescoping of the intestine, and other blockages can cause the intestine or stomach to rupture. Although sometimes these symptoms occur over a period of a day or so, some gut issues may occur quickly, resulting in acute signs that lead to sudden death.

    Continue to 5 of 5 below.
  • 05 of 05

    Congenital Defects

    Nursing foal.


    Horses can be born with congenital defects that can lead to sudden death. There may be no outward sign that anything is wrong in the foal. Depending on what the congenital defect is, the horse may survive until adulthood but suddenly die. Some cardiac defects manifest clinically this way.

If Your Horse Suddenly Dies

Necropsy (autopsy on an animal) may reveal the cause of death; this requires the expertise of a veterinarian. Providing the best care possible for your horse is the best way to help your horse live a long and comfortable life.

If you suspect your pet is sick, call your vet immediately. For health-related questions, always consult your veterinarian, as they have examined your pet, know the pet's health history, and can make the best recommendations for your pet.
Article Sources
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  1. Briceno, Abelardo Morales, Mendez, Aniceto, Brewer, Kimberly, Hughes, Charlie, Tobin, Thomas. Sudden Death, Aortic Rupture in Horses, Literature Review, Case Studies Reported and Risk Factors. Brazilian Journal of Veterinary Research and Animal Science, 52,4, 2015, doi:10.11606/issn.1678-4456.v52i4p298-309

  2. Ionophore Intoxication in Horses. University of Kentucky Agriculture, Food, and Environment.

  3. Disorders Involving Anaphylactic Reactions (Type I Reactions) in Horses. Merck Manual Veterinary Manual.

  4. Winfield, Laramie S, Dechant, Julie E. Primary Gastric Rupture in 47 Horses (1995-2011). The Canadian Veterinary Journal = La Revue Veterinaire Canadienne, 56,9,953-8, 2015