Poisonous Plant Quiz

Bracken Fern Sorry! That's the wrong answer. This is Bracken Fern. Also referred to as Eastern Bracken, this weed is found in open fields and woodlands. Leaves of Bracken Fern are poisonous to horses both when fresh and when dry in hay. Cattle are far more likely to be poisoned by Bracken than horses.

Bracken Fern contains thiaminse, which causes a deficiency in Vitamin B1 (thiamine) and which is important for proper nerve function. It would be necessary for a horse to ingest hundreds of pounds of Bracken over a week or more in order for a problem to occur. Symptoms are slow to develop.


  • loss of flesh
  • jaundice
  • loss of appetite
  • weakness
  • staggering gait
  • excitability
  • paralysis

Well-timed injections of thiamine can successfully reverse the damage caused by ingestion of Bracken Fern.

A veterinarian should be consulted immediately for supportive treatment to reduce the damage caused by ingestion of poisonous plants.

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For more information:
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E-mail: ag.info.omafra@ontario.ca

Author: Penny Lawlis - Animal Care Specialist/OMAFRA
Creation Date: Not Available
Last Reviewed: November 2003