List of plants poisonous to equines

Paterson's Curse has been responsible for the deaths of many horses.

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 (found in horses bedded on shavings from black walnut trees), anemia, kidney disease and kidney failure (from eating the wilted leaves of red maples), to cyanide poisoning (from the ingestion of plant matter from members of the genus Prunus) and other symptoms. Members of genus Prunus have also been theorized to be at fault for mare reproductive loss syndrome.[1] Some plants, including yews, are deadly and extremely fast-acting.[2] 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.[3]

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.[4] Hungry or thirsty horses are more likely to eat poisonous plants, as are those pastured on overgrazed lands.[5] Animals with mineral deficiencies due to poor diets will sometimes seek out poisonous plants.[6] Poisonous plants are more of a danger to livestock after wildfires, as they often regrow more quickly.[7]

Poisonous plants

Crofton weed (Ageratina adenophora) (flowers and leaves)

The deadly Nerium oleander

Scientific name	Common name	Notes	References
Abrus precatorius	Crab's eye	Also known as precatory bean, rosary pea, or jequirity bean	[8]
Acer rubrum	Red maple, also known as swamp or soft maple	Toxic compounds are gallic acid and tannins.	[9][4]
Adonis microcarpa	Pheasant's eye	Often found in hay.	[10][11]
Aesculus hippocastanum	Horse chestnut	Also known as buckeye	[3]
Ageratina	Snakeroots	Known poisonous species include Ageratina adenophora (Crofton weed, causes Tallebudgera horse disease) and Ageratina altissima (white snakeroot)	[3][12]
Aleurites	Tung oil tree		[8]
Amsinckia intermedia	Fiddleneck	Contains pyrrolizidine alkaloids	[13][14][15]
Apocynum cannabinum	Hemp dogbane	Also known as Indian hemp, choctaw root, rheumatism weed, and snake's milk	[5]
Arctotheca calendula	Cape weed		[10]
Armoracia lapathifolia	Horseradish		[8]
Artemisia		Known poisonous species include Artemisia tridentata (big sagebrush) and Artemisia filifolia (sand sagebrush)	[8]
Asclepias syriaca	Common milkweed		[4]
Astragalus	Locoweed, crazy weed, or milk vetch	Contains Swainsonine	[4][16]
Atropa belladonna	Deadly nightshade or belladonna		[17]
Baptisia	False indigo		[8]
Berteroa incana	Hoary alyssum		[18]
Brassica	Mustards		[5]
Buxus sempervirens	Boxwood		[3]
Celastrus scandens	Climbing bittersweet		[8]
Centaurea	Star-thistles, knapweeds	Known poisonous species include Centaurea solstitialis (yellow star thistle or St. Barnaby's thistle) and Centaurea repens (Russian knapweed)	[3][10]
Cestrum parqui	Green cestrum		[17]
Chrysothamnus nauseosus	Rubber rabbitbrush		[8]
Cicuta	Water hemlock, cowsbane		[3]
Claviceps paspali	Paspalum ergot		[10]
Conium maculatum	Hemlock or poison hemlock		[10]
Corydalis	Fitweed, fumitory		[8]
Craspedia chrysantha	Round billy button or woollyhead		[10]
Crotalaria	Rattlepods		[19]
Cucumis myriocarpus	Paddy melon		[10]
Cuscuta	Dodder		[8]
Cynoglossum officinale	Houndstongue		[6]
Datura	Jimsonweed, thorn-apple		[4][10]
Delphinium	Larkspur		[3]
Dendrocnide moroides	Stinging tree or Gympie stinger		[17]
Descurainia pinnata	Tansy mustard		[8]
Digitalis	Foxgloves		[3]
Dryopteris filix-mas	Male fern		[8]
Duboisia	Corkwoods		[17]
Echium plantagineum	Paterson's curse	Also known as Salvation Jane, blue weed and Lady Campbell weed	[10][20]
Equisetum	Horsetails, mare's tails, scouring rush		[16]
Erythrophleum chlorostachys	Cooktown ironwood		[19]
Euphorbia	Spurges		[8]
Festuca arundinacea	Tall fescue		[3]
Franseria discolor	White ragweed		[8]
Glechoma hederacea	Ground ivy	Also known as creeping charlie	[3]
Grindelia	Gumweeds		[8]
Haplopappus heterophyllus	Rayless goldenweed	Also known as jimmyweed or burrow weed	[8]
Heliotropium	Heliotropes	Known poisonous species include Heliotropium amplexicaule (blue heliotrope), H. europaeum (common heliotrope), and H. supinum (creeping heliotrope)	[10][17][21]
Homeria	Cape tulips		[22]
Hypericum perforatum	St. John's wort	Also known as Klamath weed	[3]
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	[10][23]
Jacobaea	Ragworts
Juglans nigra	Black walnut	Bedding horses in shavings or sawdust can cause laminitis	[3]
Juniperus virginiana	Juniper		[8]
Kalmia latifolia	Mountain laurel or spoonwood	Also known as spoonwood or calico bush	[17]
Kochia scoparia	Burning bush	Also known as summer cypress or Mexican firewood	[8]
Lantana camara	Yellow sage		[24]
Ligustrum	Privets		[17]
Lolium perenne	Perennial ryegrass		[10]
Lupinus	Lupins		[3]
Lychee	Lychee	Ingesting large amounts almost certainly caused the death of four horses	[25]
Malva parviflora	Mallow		[10]
Marsilea drummondii	Nardoo	Contains an enzyme which destroys vitamin B1, leading to brain damage in sheep and horses	[10]
Melilotus	Sweetclover	Includes Melilotus alba (white sweetclover) and M. officinalis (yellow sweetclover), can be grazed as a forage crop, but mold or spoilage converts coumarins to toxic dicumarol, thus moldy hay or silage is dangerous	[5]
Nerium oleander	Oleander	Also known as rose laurel, adelfa, or rosenlorbeer	[3][16]
Nicotiana	Tobacco		[17][15]
Onoclea sensibilis	Sensitive fern or meadow fern		[8][15]
Oxytropis	Locoweed or crazy weed	Contains Swainsonine	[4][16][15]
Persea americana	Avocado		[26][15]
Physalis	Japanese lanterns, groundcherries		[4][5]
Phytolacca americana	Pokeweed		[4]
Prunus	Cherries, apricots, peaches, and plums		[4][15]
Pteridium esculentum/P. aquilinum	Bracken fern		[4][10][16]
Quercus	Oaks		[1][15]
Ranunculus	Buttercups		[10]
Raphanus raphanistrum	Wild radish		[5][15]
Rhododendron	Azaleas, laurels, and rose bays		[16][15]
Ricinus communis	Castor bean	Also known as palma Christi, fatal even in small amounts	[3][16]
Robinia pseudoacacia	Black locust	Also known as false acacia	[3][4]
Romulea		Known poisonous species include Romulea longifolia (Guildford grass) and R. rosea (onion grass or onion weed)	[10][22]
Rudbeckia laciniata	Goldenglow, coneflower, or thimbleweed		[8]
Senecio	Ragworts, groundsel, or stinking willy		[4][10]
Silybum marianum	Variegated thistle	Poisons cattle, sheep, and rarely horses	[10]
Solanum	Potatoes, tomatoes, nightshades, horse nettle, ground cherry, or Jerusalem cherry		[3][4][15]
Solidago	Goldenrod		[8]
Sorghum	Sudan grass, Johnson grass	Cyanide produced after stress	[4][10][16]
Stachys arvensis	Field woundwort or stagger weed		[27]
Stipa viridula	Sleepy grass		[8]
Swainsona	Darling peas		[10]
Taraxacum officinale	Dandelion	When infected with a toxic mold that grows on it, the plant has been linked to outbreaks of Australian stringhalt.	[23]
Taxus	Yews		[16]
Trifolium pratense	Red clover		[3]
Vinca major	Blue periwinkle or large periwinkle		[10]
Wislizenia refracta	Jackass clover		[8]
Xanthium strumarium	Cocklebur		[5]
Zephyranthes atamasca	Atamasco lily or rain lily		[8]

References

1. Cable, Christina (1 April 2002). "Which Trees are Toxic?". The Horse.
2. "Poisonous Plants: Yew". Horse & Hound. 25 June 2001. Archived from the original on 18 March 2012. Retrieved 12 December 2010.
3. King, Marcia (1 May 2001). "Poisonous Plants". The Horse. Retrieved 7 December 2010.
4. DeLong, Jodi (10 October 2008). "Poisonous Plant Risk Increases as Pasture Grass Goes Dormant". The Horse.
5. "Horse Nutrition". Ohio State University. Archived from the original on 6 December 2010. Retrieved 8 December 2010.
6. Israelsen, Clark E.; McKendrick, Scott S.; Bagley, Clell V. (1 October 2006). "Poisonous Plants and Equines" (PDF). Utah State University. Archived from the original (PDF) on 12 January 2011. Retrieved 8 December 2010.
7. Knight, James E. (2002). "After Wildfire" (PDF). Montana State University. Retrieved 15 December 2010.
8. DiTomaso, Joseph M. (1994). "List of Plants Reported to be Poisonous to Animals in the United States" (PDF). 36:49–52. Veterinary and Human Toxicology. Also, plantsciences.ucdavis.edu/PlantSciences_Faculty/Ditomaso/main/pubs.htm
9. LLC, HorseDVM. "HorseDVM Toxic Plants for Horses | Red maple". HorseDVM. Retrieved 9 July 2017.
10. McBarron, E.J. (1983). Poisonous Plants. Melbourne: Inkata Press. ISBN 0-09-096029-7.
11. LLC, HorseDVM. "HorseDVM Toxic Plants for Horses | Summer pheasant's eye". HorseDVM. Retrieved 9 July 2017.
12. Jordan, Sonia (26 October 2010). "Crofton weed". The State of Queensland. Retrieved 6 December 2010.^[permanent dead link‍]
13. "Toxic Plants in Your Hay and Pasture". University of California – Davis. Archived from the original on 4 January 2011. Retrieved 7 December 2010.
14. LLC, HorseDVM. "HorseDVM Toxic Plants for Horses | Fiddleneck". HorseDVM. Retrieved 9 July 2017.
15. LLC, HorseDVM. "HorseDVM Poisonous Plants in horse pastures". HorseDVM. Retrieved 9 July 2017.
16. Lamm, Willis (1997). "Poisonous Plants". TrailBlazer Magazine. Retrieved 6 December 2010.
17. Offord, Mellisa. "Plants Poisonous to Horses: An Australian Field Guide" (PDF). Rural Industries Research and Development Corporation, Australian Government. Archived from the original (PDF) on 15 July 2011. Retrieved 8 December 2010.
18. Michigan State University Extension (17 July 2008). "Horse Owners Cautioned about Hardy Toxic Plant". The Horse. Retrieved 7 December 2010.
19. McKenzie, Ross. "Australian Native Poisonous Plants". Australian Native Plants Society. Archived from the original on 10 April 2011. Retrieved 6 December 2010.
20. "Toxic Plants for horses". Shiny Plant. Retrieved 4 December 2022.
21. "Common heliotrope" (PDF). New South Wales Department of Agriculture. May 2004. Retrieved 25 February 2017.
22. "Common pasture weeds that may poison horses". Government of South Australia. 20 November 2008. Retrieved 6 December 2010.
23. Kohnke, John. "Australian stringhalt" (PDF). South East Victoria Equine Network. Archived from the original (PDF) on 21 February 2011. Retrieved 6 December 2010.
24. "Lantana (Lantana camara L.)". University of Illinois at Urbana-Champaign. Archived from the original on 26 November 2011. Retrieved 12 December 2010.
25. "Our horses died from too many Lychees". Facebook. Retrieved 1 December 2017.
26. "Avocado". University of Pennsylvania. 2002. Archived from the original on 5 December 2010. Retrieved 7 December 2010.
27. "Important Poisonous Vascular Plants of Australia". Merck & Co., Inc. 2008. Archived from the original on 17 November 2010. Retrieved 8 December 2010.

External links

• Contact information for Animal Poison Control Center in the United States