Can they eat it? / Poison hemlock
Can horses eat poison hemlock?
Never. Looks like wild carrot; kills by paralysis.
Tall, with purple-blotched stems and a musty smell. It grows along roads and field edges and stays toxic in hay.
Trembling, weakness, drooling, slow breathing, collapse.
Call your vet now. Note what was eaten, how much and when; do not wait for signs.
Why it is dangerous
Poison hemlock (Conium maculatum) contains piperidine alkaloids, chiefly coniine and gamma-coniceine, which act on the nervous system. They block nerve signals to the muscles, so the horse loses muscle control and eventually the muscles needed to breathe weaken. The whole plant is toxic, and the alkaloids remain active when the plant dries, so it stays dangerous in hay.
How much is too much
For a 1,000 lb horse there is no amount considered safe. Even a small handful of leaves or stems can cause harm, and a larger quantity can be fatal. Ponies and miniatures are at no lower risk, since a smaller body means a smaller dose is enough. Do not judge by how little was eaten; treat any contact as an emergency.
Horses
Horses in work or at pasture are exposed mainly along fence lines, road ditches and field edges. Walk the perimeter and pull plants by the root, wearing gloves, before turnout. Check hay carefully, since dried hemlock is easy to miss among grass. Keep horses from grazing near it, and keep clippings out of the feed area.
Ponies and easy keepers
Ponies, miniatures, seniors and easy keepers can be harmed by even less plant material, and they may be more likely to nibble at unfamiliar growth. Keep these horses on well-managed grass and inspect any field before they go in. If a senior or small horse shows any sign of trouble, do not wait; call your vet right away.
Safe alternatives
Offer safe forage that you know well, such as good-quality grass hay or pasture you have checked. A measured flake of timothy or orchard grass hay gives fiber without risk. For a treat, a few slices of apple or carrot, offered by hand, are good choices.
Questions people ask
Is poison hemlock still dangerous in hay?
Yes. The alkaloids stay toxic after the plant dries, so hemlock in hay can still cause poisoning. Inspect every bale and remove any plant you find.
My horse ate some hemlock. What do I do?
Call your vet now, even if your horse looks normal. Note what was eaten, how much and when. Do not wait for signs such as trembling or drooling.
How do I tell poison hemlock from wild carrot?
Hemlock is taller, with smooth, hollow stems blotched with purple, and it has a musty smell. Because the two look alike, ask a local extension office to confirm an identification before you clear a field.
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.