Can they eat it? / Bracken fern
Can horses eat bracken fern?
No. Destroys vitamin B1 over weeks.
Horses eat it when grazing is short or when it is baled in hay. Signs come after a month or more of eating it.
Staggering, weight loss, a wide stance, tremors; treatable early with thiamine.
Call your vet; remove the horse from the pasture.
Why it is dangerous
Bracken fern contains thiaminase, an enzyme that breaks down thiamine (vitamin B1) in the body. Over weeks of regular eating, the horse's thiamine stores run down, and the nervous system begins to suffer. Ptaquiloside, a carcinogenic compound, is also present in bracken, which is why long-term exposure is a serious concern. Hay containing bracken is just as risky as fresh grazing, because the enzyme survives drying.
How much is too much
There is no safe amount of bracken fern for a horse to eat regularly. A few stray leaves from a pasture edge carry little risk in a single bite, but a handful a day over a month can cause harm. A pony or miniature horse has a smaller body and less thiamine reserve, so the damage can come on sooner. Horses on short pasture are most at risk because they graze down anything green.
Horses
Horses grazing pastures with bracken are most often affected when forage runs short in drought or after heavy grazing. Check field edges, fence lines, and wooded margins where bracken spreads. Ask about hay sources, since bracken can be baled in with grass. Keep horses on well-managed pasture with adequate grass, and remove bracken where you can reach it.
Ponies and easy keepers
Ponies, miniatures, and easy keepers often graze harder and may be turned out on rougher ground, so bracken exposure is a real concern. Seniors may have less reserve to absorb thiamine loss. Insulin-resistant or laminitis-prone animals should be kept off bracken-heavy paddocks. Watch for weight loss or stumbling, and call your vet promptly if you notice either.
Safe alternatives
Offer fresh grass hay or a grass-based pasture mix, which supply fiber and steady nutrition. Provide a salt block and clean water at all times. If pasture is short, feed an approved grass hay from a trusted source, served in a hay net or feeder to limit waste.
Questions people ask
Is bracken fern dangerous in hay?
Yes. Bracken can be baled with grass, and the thiaminase enzyme survives drying, so contaminated hay carries the same long-term risk as grazing.
My horse ate bracken fern once. Should I worry?
A single small taste is unlikely to cause harm, but watch closely for weeks. Call your vet if you notice staggering, weight loss, tremors, or a wide stance.
Can a horse recover from bracken poisoning?
Early treatment with thiamine often helps, which is why calling your vet quickly matters. Remove the horse from the pasture right away and let your vet guide the next steps.
Toxic for horses means: do not give it; if they ate it, call your vet or a poison line.
General information from veterinary guidance, not a diagnosis. If you are worried, call your vet or a pet poison line: ASPCA Animal Poison Control (888) 426-4435. Charges may apply.
Written by Hoofdeck editors · updated Nov 13, 2026 · from ASPCA Animal Poison Control, Merck Veterinary Manual and university extension guidance.