Common Causes of Sudden Death in Horses

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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. Why do horses suddenly die? Why do owners find horses dead in their pasture or stall with not a mark on them or any indication of illness or struggle? Even the most carefully looked after horses can die very suddenly.

  • 01 of 07

    Ruptured Aorta

    lamazeon hickstead

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     A ruptured aorta is caused by the weakening of a portion of the aorta wall. Also called an aortic aneurysm, it’s one of the more common aneurysms in horses. When heart rate and blood pressure increase, such as during hard exercise, or even playing in the pasture, the weak area can balloon and burst.

    The aorta is the main blood vessel coming out of the heart, so the horse quickly hemorrhages and dies. There is no warning that this will happen, and death occurs very quickly, seemingly before the horse hits the ground. Some people who have had horses die of a ruptured aorta report a small amount of blood seeping out of the nostrils after the horse is dead.

  • 02 of 07

    Cardiac Arrest

    horse in stable aisle

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    Cardiac arrest and heart failure can have a few different causes. Some problems may be congenital. Electric shock, disease, drugs, heat stroke, tumors, and viral or bacterial infections can all lead to heart failure. Some conditions make the heart muscle weaker, or stiffer, making it harder to pump blood to the body efficiently.

    The extra stress of exertion, even just playing with a pasture mate or going for a canter down the trail can lead to cardiac arrest. Sometimes heart failure can be treated, and sometimes it is fatal before anyone knows there is something wrong. Cardiac arrest isn’t as common in horses as it is in humans.

  • 03 of 07


    Red oak leaves in autumn

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    A horse can die unexpectedly and quite rapidly after ingesting any number of toxins. These can include eating various plants and tree leaves such as bracken fern, red oak, and others. Botulism and other harmful bacteria may be in fodder such as silage, or water. Some livestock feed, such as cattle and chicken feed, may be deadly to horses and cause rapid death.

  • 04 of 07

    Drug Reactions

    Horse receiving vaccination.

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    Drug reactions 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.

    Continue to 5 of 7 below.
  • 05 of 07

    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 serious problems. The first indications can appear as colic symptoms. Drinking or eating too much, parasite load, a twisting or telescoping of the intestine, and other blockages can cause the intestine or stomach to rupture. Parasites can cause a weakening of the walls of the stomach and intestinal system.

    A horse may appear to have colic and then suddenly improve. This is because the distention has ruptured and provided some temporary relief of the pain. With the release of digestive contents into the horse’s abdominal cavity, though, death will follow within a few hours.

  • 06 of 07

    Brain Aneurysm

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    A brain aneurysm is caused by a weakness in the wall of a blood vessel within the brain. The increased blood pressure from exertion can strain an aneurysm, just as it does in a ruptured aorta, causing it to burst. An aneurysm can lead to cerebral hemorrhage. Like a ruptured aorta, there is usually no indication that anything is awry before it happens. This is less common in horses than it is in humans.

  • 07 of 07

    Congenital Defects

    Nursing foal.


    Horses can be born with defects, usually of the heart, that can lead to sudden death. There is often no sign that anything is wrong, and the horse can be quite young when the defect causes a problem.

If Your Horse Suddenly Dies

If your horse dies suddenly, you shouldn't feel guilty if you've kept it in a healthy condition until that point. There is usually little warning that anything is amiss before a horse collapses. Necropsy may reveal the cause, but it is expensive. Often horses die without finding the real story for this reason. It's important to remember that horses, like every animal, including humans, sometimes just die. Very few horses quietly die of old age.

Provide the best care possible for your horse, and you'll be doing all you can to give it the best chance for a long and comfortable life.