Maple tree men­ace

The dan­ger posed by wilted or dried red maple leaves has long been known, but ev­i­dence is grow­ing that, un­der the right cir­cum­stances, other types of maple leaves can poi­son horses as well.

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Maple trees are com­monly used for land­scap­ing in many ar­eas of North Amer­ica and es­pe­cially in the north­east­ern states. Some species such as the sugar maple are eco­nom­i­cally valu­able for the pro­duc­tion of maple syrup, and wood from the trees is used for the man­u­fac­ture of fur­ni­ture and mu­si­cal in­stru­ments. How­ever, some maple species have a sin­is­ter side---horses and ponies as well as don­keys, mules and ze­bras eat­ing the fallen, wilted or dried leaves can be fa­tally poi­soned.

Although the dan­gers of poi­son­ing from one species, the red maple ( Acer rubrum, also called swamp maple or soft maple), are well known, re­search sug­gests that other trees of the species, in­clud­ing the sugar and sil­ver maples and their hy­brids, may also pose a threat. In fact, cases of maple poi­son­ing have been iden­ti­fied in horses that con­sumed wilted leaves from the sugar maple (Acer sac­cha­rum).

Horses are most likely to en­counter wilted leaves af­ter sum­mer storms bring down branches or blow leaves into pas­tures and pad­docks. In the au­tumn, fallen maple leaves are gen­er­ally less palat­able to horses, but they also pose a se­ri­ous threat when they are con­sumed. Fresh, green leaves of any maple species are less dan­ger­ous but may still con­tain some level of tox­ins. The bark and twigs of maple trees may also be toxic if con­sumed by horses.

“Red maple tox­i­c­ity is not com­mon, sim­ply be­cause most peo­ple feed their horses well and pay at­ten­tion to what their horses are eat­ing,” says An­thony Knight, BVSc, MS, DACVIM, a large an­i­mal vet­eri­nar­ian, plant tox­i­col­o­gist and pro­fes­sor emer­i­tus at Colorado State Univer­sity. “A horse may eat a few maple leaves on oc­ca­sion, but an adult horse would need to eat one to two pounds of the dried or wilted maple leaves to be af­fected by the toxin. It is the dose that makes the poi­son.”

Still, to keep your horse safe, it’s a good idea to be able to iden­tify the maple species---sugar and sil­ver as well as red maples---be­cause they are com­mon in or around pas­tures and may be en­coun­tered on the trail.

By Heléna Ragoné, PhD

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