Which plant is poisonous to horses?

• A. Dandelion
• B. Clover
• C. Grass
• D. Foxglove

Answer: (D)

Foxglove contains cardiac glycosides that are highly toxic to horses. When ingested, these compounds disrupt the heart’s electrical signals by inhibiting the sodium-potassium pump in heart cells, which raises intracellular calcium and causes the heart to beat irregularly or too forcefully. The result can be weakness, colic-like pain, rapid or irregular heartbeat, collapse, or even death, depending on the dose. Because horses may nibble ornamental plants like foxglove if they’re growing near pastured or yard areas, it’s especially dangerous.

In contrast, dandelion, clover, and ordinary grass are not regarded as poisonous to horses in typical grazing situations, so they don’t carry the same risk of severe cardiac toxicity.