Certain Maple Tree Seeds Can Kill Horses

Equine atypical myopathy and seasonal pasture myopathy are caused by eating maple tree seeds or saplings containing hypoglycin A.
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Certain Maple Tree Seeds Can Kill Horses
Acer pseudoplatanus seeds can cause atypical myopathy, a disease that is commonly fatal. | Photo: iStock

This fall the British Equine Veterinary Association (BEVA) is warning of a perfect storm of conditions that might lead to an increased incidence of the muscle condition atypical myopathy (AM) in pastured horses in Great Britain. Atypical myopathy is a sudden onset disease that’s commonly fatal. Although veterinarians have recognized it for decades, researchers only identified the cause, hypoglycin A, in 2013.

The Risk

Hypoglycin A is most typically found in the sycamore tree (Acer pseudoplatanus), a type of maple. This is not the U.S. sycamore, Platanus occidentalis. However, a similar disease known as seasonal pasture myopathy (SPM) does occur in the United States due to consumption of Acer negundo, or box elder tree (also known as a boxelder maple or, in Canada, a Manitoba maple). This condition is most prevalent in the Midwestern United States and results from horses eating the tree’s seeds. Atypical myopathy also occurs due to seed consumption but might occur when dead wood or dead leaves are consumed, as well.

The level of the toxin varies from seed to seed, so the amount of seeds needed for the disease to occur can vary from fewer than 100 to several thousand. Symptoms can occur quickly and include weakened muscles, reluctance to walk, sudden stiffness and muscle tremors, sweating, depression, high heart rate, dark urine, collapse, and colic. The fatality rate is around 70%

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Written by:

Clair Thunes, PhD, is an equine nutritionist who owns Clarity Equine Nutrition, based in Gilbert, Arizona. She works as a consultant with owners/trainers and veterinarians across the United States and globally to take the guesswork out of feeding horses and provides services to select companies. As a nutritionist she works with all equids, from WEG competitors to Miniature donkeys and everything in between. Born in England, she earned her undergraduate degree at Edinburgh University, in Scotland, and her master’s and doctorate in nutrition at the University of California, Davis. Growing up, she competed in a wide array of disciplines and was an active member of the U.K. Pony Club. Today, she serves as the district commissioner for the Salt River Pony Club.

One Response

  1. Thank you for this great info. I see that your article says the Sycamore tree that causes this condition is not the US. Sycamore. Does that mean the US Sycamore (platanus occidentalis) is safe to plant near horse pastures? I’m looking for more information on if this U.S. species is safe or not.

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