A tree with compound leaves (oval leaflets, 2-5cm in length), short thorns, fragrant white or cream flowers and large brown leathery pods with 5-9 seeds. The toxin is present in the bark, seeds and leaves. 0.04% body weight is toxic to a horse. Signs of toxicity include colic/diarrhea, weakness, increased respiratory rate, depression, increased heart rate.
Buttercups: a common pasture weed, not extremely toxic. Contains an irritating compound which, when ingested in sufficient quantities, may cause salivation, decreased appetite, depression, diarrhea or colic.
Foxglove: A tall flowering plant with tubular flowers, up to 3 inches in length, which droop down. Flowers are usually pink or purple (rarely white) and usually spotted on the inside. The toxin affects the heart, causing arrhythmias, weakness, heart failure and death. Colic/diarrhea may also be seen.
Rhododendron: A large ornamental shrub with large, oblong, smooth leathery evergreen leaves. Toxin is in the leaves and flower nectar. 0.2% body weight of the leaves or 3 ml of the nectar per kilogram body weight is toxic/lethal. Signs include salivation, diarrhea, muscle weakness, impaired vision, slow heart rate and heart block (which may be lethal). Difficulty breathing and depression may also be seen.
Chokecherry: A common pasture weed which is lethal in sufficient concentration (100g of leaves per 100lb of body weight). Stems, leaves and seeds all contain cyanide, especially when wilted. The signs of toxicity include brick-red mucous membranes, dilated pupils, difficulty breathing, shock, muscle tremors, convulsions and death.
Yew: a highly toxic ornamental shrub. Causes tremors, muscle weakness, difficulty breathing, collapse and sudden death due to heart failure. 6-8 oz of the fresh plant is enough to kill an adult horse. The entire plant, except for the red fruit, is toxic.
Black Walnut: A tree native to northeast US and Canada. Compound leaves, spherical fruit with a green, thick husk. Toxic to horses when it is included in bedding; as little as 5% in the shavings can be toxic. Ingested nuts or hulls have also been implicated as causing signs. Signs of toxicity are seen within 24 hours after exposure, and include depression, inappetance, stocked-up limbs, rapid onset of laminitis. Increased temperature, heart rate, respiratory rate and mild colic may also be seen.