Plants Poisonous to Horses: Reference Chart

Treat it as an emergency and call your veterinarian immediately, and consider the ASPCA Animal Poison Control Center at (888) 426-4435 (a consultation fee may apply). Try to identify the plant and note how much and when, and save a sample if you can. Do not wait for signs to appear, because some toxins like yew and oleander can be fatal quickly. Keep the horse calm, remove access to the plant, and follow your vet's instructions exactly.

Wilted or dried red maple leaves, often after a storm drops branches or in fall, contain toxins that damage red blood cells and cause severe hemolytic anemia. Fresh green leaves on the tree are far less of a concern; the danger comes from wilted and dead leaves. Signs include dark red or brown urine, pale or yellow gums, weakness, and rapid breathing. It can be fatal, so remove fallen maple branches from pastures and call your vet at once if exposure is suspected.

Yew is one of the deadliest plants for horses. Every part except the fleshy berry covering contains taxine alkaloids that disrupt the heart, and even a small mouthful of clippings can kill a horse within hours, often with sudden death and few warning signs. Hedge trimmings tossed over a fence are a classic cause. Never plant yew near horses and never dump yard clippings into a paddock. Suspected ingestion is a dire emergency requiring an immediate vet.

Yes, in quantity. Acorns, oak leaves, and buds contain tannins that can cause colic, diarrhea, and kidney damage when eaten in large amounts, and some horses develop a taste for fallen acorns in autumn. Most horses are fine with incidental nibbling, but heavy acorn drops are a real risk. Fence horses away from oak trees during acorn season, pick up or clear heavy falls, and provide plenty of forage so horses are less tempted to forage acorns.

Ragwort and related tansy plants contain pyrrolizidine alkaloids that cause cumulative, irreversible liver damage. The danger is insidious because horses usually avoid the bitter living plant but readily eat it dried in hay, where it is just as toxic and harder to spot. Damage builds over time, so signs like weight loss, photosensitivity, and behavioral changes may appear long after exposure. Remove ragwort from pastures and hayfields and inspect hay carefully.

Some plants act fast and can kill within hours, including yew, oleander, and large doses of red maple leaves, because they hit the heart or blood directly. Others cause slow, cumulative damage, especially ragwort and tansy (liver) and bracken fern (thiamine depletion over weeks). Either pattern is serious. Fast toxins are an immediate life-threatening emergency, while slow toxins often go unnoticed until significant organ damage has occurred, which is why prevention and hay inspection matter.

Walk your pastures and fence lines regularly to identify and remove toxic plants, and learn the dangerous species in your region. Provide ample good forage so bored or hungry horses are less likely to sample weeds. Never dump garden or hedge clippings, especially yew or oleander, where horses can reach them. Inspect purchased hay for dried ragwort and other weeds. When clearing toxic plants, remove and dispose of them fully, since some stay dangerous after wilting or drying.