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. 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.
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. This information is provided as a public service, but we cannot guarantee that the information is current or accurate. Readers should verify the information before acting on it.