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 tissue damage. Members of genus Prunus had been theorized to be at fault for mare reproductive loss syndrome, but the eastern tent caterpillar was later found to be the cause. 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 ReferencesAbrus precatoriusCrab's eyeAlso known as precatory bean, rosary pea, or jequirity beanAcer rubrumRed maple, also known as swamp or soft mapleToxic compounds are gallic acid and tannins.Adonis microcarpaPheasant's eyeOften found in hay.Aesculus hippocastanumHorse chestnutAlso known as buckeyeAgeratinaSnakerootsKnown poisonous species include Ageratina adenophora (Crofton weed, causes Tallebudgera horse disease) and Ageratina altissima (white snakeroot)AleuritesTung oil treeAmsinckia intermediaFiddleneckContains pyrrolizidine alkaloidsApocynum cannabinumHemp dogbaneAlso known as Indian hemp, choctaw root, rheumatism weed, and snake's milkArctotheca calendulaCape weedArmoracia lapathifoliaHorseradishArtemisiaKnown poisonous species include Artemisia tridentata (big sagebrush) and Artemisia filifolia (sand sagebrush) Also, plantsciences.ucdavis.edu/PlantSciences_Faculty/Ditomaso/main/pubs.htmAsclepias syriacaCommon milkweedAstragalusLocoweed, crazy weed, or milk vetchContains SwainsonineAtropa belladonnaDeadly nightshade or belladonnaBaptisiaFalse indigoBerteroa incanaHoary alyssumBrassicaMustardsBuxus sempervirensBoxwoodCelastrus scandensClimbing bittersweetCentaureaStar-thistles, knapweedsKnown poisonous species include Centaurea solstitialis (yellow star thistle or St. Barnaby's thistle) and Centaurea repens (Russian knapweed)Cestrum parquiGreen cestrumChrysothamnus nauseosusRubber rabbitbrushCicutaWater hemlock, cowsbaneClaviceps paspaliPaspalum ergotConium maculatumHemlock or poison hemlockCorydalisFitweed, fumitoryCraspedia chrysanthaRound billy button or woollyheadCrotalariaRattlepodsCucumis myriocarpusPaddy melonCuscutaDodderCynoglossum officinaleHoundstongueDaturaJimsonweed, thorn-appleDelphiniumLarkspurDendrocnide moroidesStinging tree or Gympie stingerDescurainia pinnataTansy mustardDigitalisFoxglovesDryopteris filix-masMale fernDuboisiaCorkwoodsEchium plantagineumPaterson's curseAlso known as Salvation Jane, blue weed and Lady Campbell weedEquisetumHorsetails, mare's tails, scouring rushErythrophleum chlorostachysCooktown ironwoodEuphorbiaSpurgesFestuca arundinaceaTall fescueFranseria discolorWhite ragweedGlechoma hederaceaGround ivyAlso known as creeping charlieGrindeliaGumweedsHaplopappus heterophyllusRayless goldenweedAlso known as jimmyweed or burrow weedHeliotropiumHeliotropesKnown poisonous species include Heliotropium amplexicaule (blue heliotrope), H. europaeum (common heliotrope), and H. supinum (creeping heliotrope)HomeriaCape tulipsHypericum perforatumSt. John's wortAlso known as Klamath weedHypochaeris radicataFlatweed or catsearHas been implicated in causing Australian stringhalt, possibly due to a toxic mold that grows on it, especially poisonous to draft horsesJacobaeaRagwortsJuglans nigraBlack walnutBedding horses in shavings or sawdust can cause laminitisJuniperus virginianaJuniperKalmia latifoliaMountain laurel or spoonwoodAlso known as spoonwood or calico bushKochia scopariaBurning bushAlso known as summer cypress or Mexican firewoodLantana camaraYellow sageLigustrumPrivetsLupinusLupinsLychee LycheeIngesting large amounts almost certainly caused the death of four horsesMalva parvifloraMallowMarsilea drummondiiNardooContains an enzyme which destroys vitamin B1, leading to brain damage in sheep and horsesMelilotusSweetcloverIncludes 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 dangerousNerium oleanderOleanderAlso known as rose laurel, adelfa, or rosenlorbeerNicotianaTobaccoOnoclea sensibilisSensitive fern or meadow fernOxytropisLocoweed or crazy weedContains SwainsoninePersea americanaAvocadoPhysalisJapanese lanterns, groundcherriesPhytolacca americanaPokeweedPrunusCherries, apricots, peaches, and plumsPteridium esculentum/P. aquilinumBracken fernQuercusOaksRanunculusButtercupsRaphanus raphanistrumWild radishRhododendronAzaleas, laurels, and rose baysRicinus communisCastor beanAlso known as palma Christi, fatal even in small amountsRobinia pseudoacaciaBlack locustAlso known as false acaciaRomuleaKnown poisonous species include Romulea longifolia (Guildford grass) and R. rosea (onion grass or onion weed)Rudbeckia laciniataGoldenglow, coneflower, or thimbleweedSenecioRagworts, groundsel, or stinking willySilybum marianumVariegated thistlePoisons cattle, sheep, and rarely horsesSolanumPotatoes, tomatoes, nightshades, horse nettle, ground cherry, or Jerusalem cherrySolidagoGoldenrodSorghumSudan grass, Johnson grass Cyanide produced after stressStachys arvensisField woundwort or stagger weedStipa viridulaSleepy grassSwainsonaDarling peasTaraxacum officinaleDandelionWhen infected with a toxic mold that grows on it, the plant has been linked to outbreaks of Australian stringhalt.TaxusYewsTrifolium pratenseRed cloverVinca majorBlue periwinkle or large periwinkleWislizenia refractaJackass cloverXanthium strumariumCockleburZephyranthes atamascaAtamasco lily or rain lily
References
External links Contact information for Animal Poison Control Center in the United States