Can they eat it? / White snakeroot
Can horses eat white snakeroot?
No. Shaded woodland edges in the eastern US; muscle and heart damage.
Eaten in late summer and fall when pasture is short. The toxin passes into milk, so nursing foals are at risk too.
Trembling, stiffness, sweating, a slow heartbeat, inability to swallow.
Call your vet now. Note what was eaten, how much and when; do not wait for signs.
Why it is dangerous
White snakeroot contains tremetol and related compounds, which are metabolized in the liver and release toxic byproducts that spread through the body. The main damage falls on skeletal muscle and heart muscle, causing a condition called trembles or milk sickness. The toxin is stable, so it stays dangerous when the plant is dried in hay or wilted, and it passes into milk, which is why nursing foals can be affected too.
How much is too much
No amount of white snakeroot is considered safe for horses, so a nibble and a mouthful are both reasons to call your vet. A full-size horse can be harmed by a relatively small quantity eaten over time, and effects are harder to reverse once signs appear. Ponies, miniatures and seniors may show trouble sooner. If you are unsure how much was eaten, treat it as enough to call about.
Horses
Horses in work or at pasture are most at risk in late summer and fall, when shaded woodland edges and fence lines stay green while open pasture dries up. Check field borders and hedgerows, keep horses off areas where the plant grows, and walk pastures before turnout. Do not rely on hay to be free of the plant, since dried snakeroot stays toxic.
Ponies and easy keepers
Ponies, miniatures, seniors and easy keepers can be harmed by the same toxin, and a small body weight leaves less margin for error. Check any woodland edge or shaded paddock you use, especially in fall. If a nursing mare or foal may have eaten it, contact your vet promptly, because the milk carries the toxin.
Safe alternatives
Keep horses on open, well-managed pasture with grass and grass hay, and mow or pull the plant where it appears. Offer fresh grass hay as the forage base when pasture thins in fall. A measured ration of hay pellets or a balanced feed can cover any shortfall, but ask your vet or extension service about the right amounts for your horse.
Questions people ask
Is white snakeroot in hay dangerous?
Yes. The toxin stays active after the plant is dried, so snakeroot in hay can still cause harm. Inspect hay carefully and remove any plants you find.
What should I do after a frost?
Frost can make the plant more attractive as other forage dies back. Check fields and borders after frost and keep horses off any patches of snakeroot.
My foal ate some, what now?
Call your vet right away, even if the foal looks fine. The toxin passes through milk, so the foal and mare both need assessment without waiting for signs.
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.