List of plants poisonous to equines
Many plants are poisonous to equines; the species vary depending on location, climate, and grazing conditions. In many cases, entire genera are poisonous to equines and include many species spread over several continents. Plants can cause reactions ranging from laminitis, anemia, kidney disease and kidney failure, to cyanide poisoning and other symptoms. Members of genus Prunus have also been theorized to be at fault for mare reproductive loss syndrome. Some plants, including yews, are deadly and extremely fast-acting. Several plants, including nightshade, become more toxic as they wilt and die, posing a danger to horses eating dried hay or plant matter blown into their pastures.
The risk of animals becoming ill during the fall is increased, as many plants slow their growth in preparation for winter, and equines begin to browse on the remaining plants. Many toxic plants are unpalatable, so animals avoid them where possible. However, this is not always the case; locoweeds, for example, are addictive and once a horse has eaten them, it will continue to eat them whenever possible, and can never be exposed to them again. When a toxic plant is ingested, it can be difficult to diagnose, because exposure over time can cause symptoms to occur after the animal is no longer exposed to the plant. Toxins are often metabolized before the symptoms become obvious, making it hard or impossible to test for them. Hungry or thirsty horses are more likely to eat poisonous plants, as are those pastured on overgrazed lands. Animals with mineral deficiencies due to poor diets will sometimes seek out poisonous plants. Poisonous plants are more of a danger to livestock after wildfires, as they often regrow more quickly.
Poisonous plants
| Scientific name | Common name | Notes | References |
| Abrus precatorius | Crab's eye | Also known as precatory bean, rosary pea, or jequirity bean | |
| Acer rubrum | Red maple, also known as swamp or soft maple | Toxic compounds are gallic acid and tannins. | |
| Adonis microcarpa | Pheasant's eye | Often found in hay. | |
| Aesculus hippocastanum | Horse chestnut | Also known as buckeye | |
| Ageratina | Snakeroots | Known poisonous species include Ageratina adenophora and Ageratina altissima | |
| Aleurites | Tung oil tree | ||
| Amsinckia intermedia | Fiddleneck | Contains pyrrolizidine alkaloids | |
| Apocynum cannabinum | Hemp dogbane | Also known as Indian hemp, choctaw root, rheumatism weed, and snake's milk | |
| Arctotheca calendula | Cape weed | ||
| Armoracia lapathifolia | Horseradish | ||
| Artemisia | Known poisonous species include Artemisia tridentata and Artemisia filifolia | ||
| Asclepias syriaca | Common milkweed | ||
| Astragalus | Locoweed, crazy weed, or milk vetch | Contains Swainsonine | |
| Atropa belladonna | Deadly nightshade or belladonna | ||
| Baptisia | False indigo | ||
| Berteroa incana | Hoary alyssum | ||
| Brassica | Mustards | ||
| Buxus sempervirens | Boxwood | ||
| Celastrus scandens | Climbing bittersweet | ||
| Centaurea | Star-thistles, knapweeds | Known poisonous species include Centaurea solstitialis and Centaurea repens | |
| Cestrum parqui | Green cestrum | ||
| Chrysothamnus nauseosus | Rubber rabbitbrush | ||
| Cicuta | Water hemlock, cowsbane | ||
| Claviceps paspali | Paspalum ergot | ||
| Conium maculatum | Hemlock or poison hemlock | ||
| Corydalis | Fitweed, fumitory | ||
| Craspedia chrysantha | Round billy button or woollyhead | ||
| Crotalaria | Rattlepods | ||
| Cucumis myriocarpus | Paddy melon | ||
| Cuscuta | Dodder | ||
| Cynoglossum officinale | Houndstongue | ||
| Datura | Jimsonweed, thorn-apple | ||
| Delphinium | Larkspur | ||
| Dendrocnide moroides | Stinging tree or Gympie stinger | ||
| Descurainia pinnata | Tansy mustard | ||
| Digitalis | Foxgloves | ||
| Dryopteris filix-mas | Male fern | ||
| Duboisia | Corkwoods | ||
| Echium plantagineum | Paterson's curse | Also known as Salvation Jane, blue weed and Lady Campbell weed | |
| Equisetum | Horsetails, mare's tails, scouring rush | ||
| Erythrophleum chlorostachys | Cooktown ironwood | ||
| Euphorbia | Spurges | ||
| Festuca arundinacea | Tall fescue | ||
| Franseria discolor | White ragweed | ||
| Glechoma hederacea | Ground ivy | Also known as creeping charlie | |
| Grindelia | Gumweeds | ||
| Haplopappus heterophyllus | Rayless goldenweed | Also known as jimmyweed or burrow weed | |
| Heliotropium | Heliotropes | Known poisonous species include Heliotropium amplexicaule, H. europaeum, and H. supinum | |
| Homeria | Cape tulips | ||
| Hypericum perforatum | St. John's wort | Also known as Klamath weed | |
| Hypochaeris radicata | Flatweed or catsear | Has been implicated in causing Australian stringhalt, possibly due to a toxic mold that grows on it, especially poisonous to draft horses | |
| Jacobaea | Ragworts | ||
| Juglans nigra | Black walnut | Bedding horses in shavings or sawdust can cause laminitis | |
| Juniperus virginiana | Juniper | ||
| Kalmia latifolia | Mountain laurel or spoonwood | Also known as spoonwood or calico bush | |
| Kochia scoparia | Burning bush | Also known as summer cypress or Mexican firewood | |
| Lantana camara | Yellow sage | ||
| Ligustrum | Privets | ||
| Lolium perenne | Perennial ryegrass | ||
| Lupinus | Lupins | ||
| Lychee | Lychee | Ingesting large amounts almost certainly caused the death of four horses | |
| Malva parviflora | Mallow | ||
| Marsilea drummondii | Nardoo | Contains an enzyme which destroys vitamin B1, leading to brain damage in sheep and horses | |
| Melilotus | Sweetclover | Includes Melilotus alba and M. officinalis, can be grazed as a forage crop, but mold or spoilage converts coumarins to toxic dicumarol, thus moldy hay or silage is dangerous | |
| Nerium oleander | Oleander | Also known as rose laurel, adelfa, or rosenlorbeer | |
| Nicotiana | Tobacco | ||
| Onoclea sensibilis | Sensitive fern or meadow fern | ||
| Oxytropis | Locoweed or crazy weed | Contains Swainsonine | |
| Persea americana | Avocado | ||
| Physalis | Japanese lanterns, groundcherries | ||
| Phytolacca americana | Pokeweed | ||
| Prunus | Cherries, apricots, peaches, and plums | ||
| Pteridium esculentum/P. aquilinum | Bracken fern | ||
| Quercus | Oaks | ||
| Ranunculus | Buttercups | ||
| Raphanus raphanistrum | Wild radish | ||
| Rhododendron | Azaleas, laurels, and rose bays | ||
| Ricinus communis | Castor bean | Also known as palma Christi, fatal even in small amounts | |
| Robinia pseudoacacia | Black locust | Also known as false acacia | |
| Romulea | Known poisonous species include Romulea longifolia and R. rosea | ||
| Rudbeckia laciniata | Goldenglow, coneflower, or thimbleweed | ||
| Senecio | Ragworts, groundsel, or stinking willy | ||
| Silybum marianum | Variegated thistle | Poisons cattle, sheep, and rarely horses | |
| Solanum | Potatoes, tomatoes, nightshades, horse nettle, ground cherry, or Jerusalem cherry | ||
| Solidago | Goldenrod | ||
| Sorghum | Sudan grass, Johnson grass | Cyanide produced after stress | |
| Stachys arvensis | Field woundwort or stagger weed | ||
| Stipa viridula | Sleepy grass | ||
| Swainsona | Darling peas | ||
| Taraxacum officinale | Dandelion | When infected with a toxic mold that grows on it, the plant has been linked to outbreaks of Australian stringhalt. | |
| Taxus | Yews | ||
| Trifolium pratense | Red clover | ||
| Vinca major | Blue periwinkle or large periwinkle | ||
| Wislizenia refracta | Jackass clover | ||
| Xanthium strumarium | Cocklebur | ||
| Zephyranthes atamasca | Atamasco lily or rain lily |