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What is Box Elder Poisoning?

Horses that develop box elder poisoning are generally kept on sparse pastures that have an accumulation of dead leaves, trees and dead wood in the pasture. Many times a horse that suffers from box elder poisoning will not survive past 72 hours of showing ingestion. There are no known treatments for box elder poisoning.

Box elder poisoning in horses is many times referred to as seasonal pasture myopathy or SPM. Horses that ingest box elder will develop a highly fatal muscle disease. The symptoms set in so quickly that many times there is no time to seek veterinarian help.

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Symptoms of Box Elder Poisoning in Horses

If you suspect that your horse is suffering from symptoms of box elder poisoning, contact your veterinarian immediately for an emergency visit. Many times these symptoms present quickly and death occurs before a veterinarian can get to your horse for care. It is important to check your pastures daily for any signs of box elder trees and remove them from your horse’s reach. Watch for these symptoms and seek immediate help:

  • Muscle weakness
  • Reluctance to move
  • Recumbency or being unable to stand after lying down
  • Stiffness 
  • Fine muscle tremors
  • Tachycardia or irregular and overly rapid heartbeat
  • Choking as if an esophageal obstruction is present
  • Rapid respiratory rate
  • Dyspnea or difficulty breathing
  • Death

Causes of Box Elder Poisoning in Horses

The ingestion of box elder seeds is what causes your horse to experience severe medical symptoms and even death. The seeds contain a toxin called hypoglycin A and it is associated with the onset of box elder poisoning, more commonly referred to as seasonal pasture myopathy. 

Box elder poisoning is more prevalent in the fall when the box elder trees lose their leaves and drop their seeds. This condition can also be prevalent in the spring if your horse is on a pasture that is sparse and they are foraging for grasses.

Diagnosis of Box Elder Poisoning in Horses

Your veterinarian will begin with a physical examination of your horse as well as looking into your horse’s past medical history. A walk through of your horse’s pasture may also be necessary to look for any signs of box elder trees and their seeds. Your veterinarian will want to examine your horse’s feed and will need a full description of their ingestion history. 

The clinical symptoms, along with laboratory analysis, will help in definitively diagnosing box elder poisoning. There are no specific tests available to identify the toxin hypoglycin A, but liver enzymes and renal functions are often elevated pointing towards poisoning. A blood smear may also show hemolytic anemia. This will show a decrease in packed cell volume.

Box elder poisoning should not be diagnosed until your veterinarian has looked at all other possible options.

Treatment of Box Elder Poisoning in Horses

There are no known effective treatments for box elder poisoning. If your veterinarian is able to diagnose box elder poisoning before it becomes fatal, they may try the same treatments that are used for red oak poisoning to try and slow the poison within your horse’s system.

Activated charcoal and mineral oil may be administered to absorb the poison that is still present within the gastrointestinal tract. These should be administered by a nasogastric tube to ensure that active charcoal and mineral oil are directly put into the stomach for the best chance of absorption.

Supportive care including intravenous fluids to help your horse excrete the toxins and decrease the acute onset of kidney damage will be required. This will help keep your horse hydrated. 

Keeping your horse calm is essential because they will not understand why their muscles are failing them. Vitamin C and Vitamin K may also be administered to help stabilize RBCs. Oxygen therapy may be needed if your horse is experiencing respiratory distress.

Recovery of Box Elder Poisoning in Horses

There is no cure and no treatment for box elder poisoning. With supportive care, some horses will be lucky enough to recover, however, for a majority of horses death usually occurs within 72 hours. Death ensues in about 75% of horses affected by box elder poisoning. 

Young horses and those who are new to a pasture that is affected by box elder trees are at a greater risk of poisoning. This is especially true if the pasture is overgrazed in the fall and early spring and there is no supplemental hay provided.

Prevention is important to keep your horse healthy. Go through your horse’s pasture at least once a week, especially in the fall and early spring. Remove any trees or shrubs that may be toxic to your horse or remove your horse from that pasture.