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Field horsetail and brackenfern: harmful plants to horses

  • Field horsetail grows in wet soils and is hard to control.

  • Brackenfern grows in open pastures and woodlands and is controlled by multiple herbicide treatments.

  • A 20 to 25 percent diet of field horsetail and brackenfern for three weeks can cause neurological problems in horses.

  • Neurologic signs include unsteady gait, twitching, depression and constipation.

  • An initial 0.5 to 1 gram dose of thiamine and decreasing daily doses can treat poisoning.

Field horsetail

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Brackenfern

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Toxicity

Brackenfern and horsetail are toxic when horses eat it fresh (in pasture) or dried in hay. If horses eat a diet with 20 to 25 percent brackenfern or field horsetail for about three weeks, neurological signs may occur. Clinical signs may occur a week to ten days if horses eat a diet nearly 100 percent brackenfern or field horsetail.

Brackenfern contains an enzyme that causes neurological syndrome in horses. Field horsetail affects horses similarly.

Signs of poisoning

  • Depression

  • Constipation

  • Unsteady gait (usually in one to two days)

Clinical signs progress to:

  • Unsteady gait

  • Muscle twitching

  • Going down

  • Paddling

  • Seizing

These signs occur for a period of a week or more.

Treatment

Horses will need an initial dose of 0.5 to 1 gram of thiamine. They will then need decreasing daily doses for three to five days.

Krishona Martinson, equine Extension specialist; Lynn Hovda, DVM, adjunct assistant professor, College of Veterinary Medicine; and Mike Murphy, DVM, former professor, College of Veterinary Medicine

Photos provided by University of Minnesota Strand Memorial Herbarium.

Reviewed in 2018

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