Often when animals consume poisonous plants, it is discovered after the damage occurs. Preventing animals from access and ingestion of toxic plants is always better than trying to treat the problem later.
Readers in other geographic locations should refer to botanical names to determine if plants are common to their area
References at the end of the article include material with more global information
Often when animals consume poisonous plants, it is discovered after the damage occurs. Preventing animals from access and ingestion of toxic plants is always better than trying to treat the problem later. Poisoning of livestock is relatively uncommon in the United States. Many times, animals will ignore toxic plants in the pasture until there is stress of some kind, either to the pasture or the animal, and feed becomes scarce.
To reduce poisoning risks:
- Learn poisonous plants in your area and take steps to eliminate them from pastures and fields.
- Keep animals out of unimproved pasture areas that might contain poisonous plants.
- Ensure adequate supplies of pasture and/or supplemental feeds.
- Keep animals away from “trimmings” and other yard/garden residues. Many poisonous plants are commonly used in landscaping.
A partial list of North American plants that are toxic to cattle (and most other animal species):
Acorns (Quercus spp.)
- toxic principle is tannic acid
- often a problem during drought conditions
- Oak leaves and buds consumed in the spring can also cause problems
- symptoms include: irritated digestive tract, emaciation, swelling, rough haircoat, depression and kidney failure
Black Locust (Robinia pseudoacacia)
- a phytotoxin, robinin, is one of the toxic elements
- commonly used lumber for fencing
- poisonous parts include the bark, leaves and seeds.
- horses are more sensitive to toxicity than cattle
- symptoms include: weakness, diarrhea, bloody feces, paralysis and rapid pulse.
- not usually fatal
Bracken Fern (Pteridium aquilinum)
- thiaminase is one of the toxic elements
- leaves above the ground are poisonous
- usually found in hay; problems occur when fed over a period of time
- requires a large amount to produce symptoms
- grows on hillsides, burned areas, shaded areas and pastures
- symptoms in cattle include hemorrhagic syndrome and sudden death
Broom Snakeweed or Threadleaf Snakeweed (Gutierrezia spp.)
- contains saponin toxins
- plant is most toxic during leaf formation and early growing period
- cattle won't choose to eat unless other feed is scarce
- symptoms include: abortion, weakness, nasal discharge, bloody urine, vaginal discharge
Buckeye or Horsechestnut (Aesculus spp.)
- toxic principle is aesculin, a glycoside
- animal can be poisoned by eating the young plant in the spring or the seeds in the fall.
- most commonly found along streams or the edges of woods
- symptoms include: weakness, dilated pupils, "drunk" or staggering gait, trembling and paralysis
Castor Bean (Ricinus communis)
- toxic principle is ricin, a deadly poison
- leaves and seeds are most poisonous
- poisoning usually occurs when grain supplies become contaminated with castor bean seeds.
- the lethal dose for a human is only one or two beans
- symptoms include: diarrhea, blood in feces, weakness, tremors, convulsions and death
Chokecherry (Prunus spp.)
- causes prussic acid poisoning (hydrocyanic acid)
- grows in moisture, usually as a result of overgrazing or drought
- leaves are the most toxic part (4. oz will kill a sheep in 30 minutes).
- wilting, bruising or frost damage increases toxicity
- symptoms include: nervousness, abnormal breathing, trembling, jerking, blue discoloration of membranes, spasms, convulsions and respiratory failure
Coffeeweed and Sicklepod (Senna occidentalis & obtusifolia)
- toxic principle is unknown
- commonly found in southern region of U.S.
- a problem in fields used for row crops (i.e. corn fields)
- Coffeeweed is more toxic, but Sicklepod is more common
- animals are more likely to eat it after damage by either mowing or frost
- affected animals are weak & unable to stand. Urine may be coffee olored initially.
- sometimes affected animals are alert but will not stand
- usually fatal
Deathcamas (Zigadenus spp.)
- contains steriodal alkaloids that cause cardiovascular failure
- all plant parts are toxic
- most commonly found in the southwestern region of the U.S.
- poisonings usually occur in the spring when it is abundant
- symptoms include: salivation and frothing, weakness, convulsions, coma and death
- death often occurs within a couple of days, sometimes within hours
Goosefoot (Chenopodium spp.)
Horsechestnut (Aesculus spp.)
- see 'Buckeye or Horsechestnut'
Horsenettle (Solanum spp.)
- toxic principle is glucoside solanine
- found in old fields, roadsides, pastures and farmyards
- leaves and berries are poisonous
- Animals consume it most often in July and August when pasture is slow growing
- Causes "crazy cow syndrome" - cattle fall when making rapid movements, are unable to rise and roll head or hold it sideways.
- Additional symptoms include: dilation of pupils, labored breathing and paralysis, and abdominal pain and diarrhea.
Jimsonweed (Datura spp.)
- also called thornapple in some parts of the US
- toxic principle is an alkaloid compound
- flowers, leaves and seeds are poisonous
- symptoms include thirst, ataxia (incoordination), blurred vision, fever, weak and rapid pulse and convulsions.
Johnsongrass (Sorghum halpense)
- toxic principle is cyanide
- cyanide prevents cells from utilizing oxygen properly
- toxicity is worse in rapidly growing and damaged plants; mature and dried plants have much lower levels
- symptoms include: labored breathing, weakness, convulsions, coma and death
Klamath weed (Hypericum perforatum)
Lamb's Quarters (Chenopodium spp.)
- also called 'Goosefoot'
- accumulates high levels of nitrates and oxalates
- animals must consume large quantities to exhibit signs of poisoning
- symptoms include: labored breathing, weakness, convulsions, coma and death
Lantana or Yellow Sage (Lantana camara)
- toxic principle is lantadene A & B, a terpenoid
- commonly grown ornamental in the Southern U.S.
- symptoms include: weight loss, lesions around the nose and mouth, liver and kidney damage & photosensitivity
Larkspur (Delphinium spp.)
- found primarily in Western U.S. states
- contains various alkaloid compounds
- especially toxic to cattle
- highly palatable, increases in palatability as it matures
- young leaves and seeds most toxic
- remains toxic when dried in hay
- symptoms include: nervousness, staggering, salivating, bloating, rapid pulse, difficulty breathing, convulsion.
- may be fatal
Locoweed (Astragalus spp.)
- contains neurotoxins
- also causes abortions, birth defects and heart failure
- grows in semiarid desert regions
- relatively palatable
- signs of poisoning usually occur after 2-3 weeks of continuous grazing although poisoning is not usually fatal, neurological damage can be permanent
- symptoms include: weakness, rough hair coat, staring eyes, emaciation, muscle incoordination and abortion
Milkweed (eastern whorled & horsetail) (Asclepias verticillata & subverticillata)
- toxic principle is glycoside
- entire plant is poisonous at all stages of growth
- only eaten by hungry animals with no alternative feed
- poisoning is more common from hay than from pasture
- symptoms include: loss of muscular control, staggering, spasms, bloating, weak and rapid pulse and respiratory paralysis.
Nightshade varieties (Solanum spp.)
Perilla Mint (Perilla frutescens)
- toxic principles are ketones
- found mainly in Southeast regions; plant prefers shady areas
- causes most problems in late summer and fall
- symptoms include: labored breathing, nasal discharge and death
Pokeweed (Phytolacca americana)
- contains saponin toxins and alkaloids
- not very palatable, most poisonings occur when grain rations become contaminated
- symptoms include: abdominal pain, salivation and diarrhea
Ponderosa Pine (Pinus ponderosa)
- toxic principle is isocupressic acid
- causes abortion in cattle when needles are consumed
- both dry and green needles cause abortions
- grows primarily in Western U.S. and Canada
- cattle are more likely to graze needles during snow storms or conditions where other feed sources are scarce
- other symptoms include: fever, retained placenta, endometritis, weak calves
Oleander (Nerium oleander)
- toxic principle is a cardiac glycoside
- commonly found ornamental plant
- poisoning often occurs when animals gain access to clippings
- leaves and stems cause toxicity
- smoke from burning the plant can also cause toxicity
- symptoms include: abdominal pain, bloody diarrhea, trembling, paralysis, coma and death
Pigweed (Amaranthus spp.)
- toxic principles are oxalates and a nephrotoxin
- often grows in fields, barnyards and waste areas
- leaves, stems and roots are poisonous
- causes kidney failure and/or nitrate poisoning
- fairly palatable; treatment with herbicide may actually increase the palatability of this plant
- symptoms include: breathing difficulty, trembling, weakness, coma, death
Rhododendron (Rhododendron spp.)
- contains at least two known toxic principles
- commonly found ornamental shrub
- flowers, leaves and immature stems are toxic to cattle
- access to clippings can cause toxicity
- pasture poisoning often occurs during winter or spring
- symptoms include: abdominal pain, low blood pressure and weakness, lack of coordination, paralysis and death
Sicklepod (Senna obtusifolia)
- see 'Coffeeweed and Sicklepod'
Sneezeweed (Helenium spp.)
- dugaldin is the toxic principle
- all plant parts are poisonous
- common in mountain ranges of Western U.S.
- sheep are more likely to be affected than cattle
- symptoms include: wasting, staggering, nasal discharge, coughing, frothing at the mouth, liver damage and bloat
- animal can die if it consumes small quantities over a long period
Snow on the Mountain (Euphorbia marginata)
- contain acrid juice
- ingestion is rarely fatal
- symptoms include: irritation of the mouth and gut, abdominal pain, diarrhea
St. Johnswort (Hypericum perforatum)
- contains photosensitizing compound, hypericin
- commonly found in Pacific coastal states of U.S.
- causes extreme photosensitivity and sunburning on hairless or white areas of the animal
- udders and teats of cattle can be severly affected, causing lactation to decrease or stop
- not palatable; animals will only eat if no other forage is available
- remains toxic after drying as hay
- other symptoms include: fever, swollen eyelids, sloughing of skin
Thornapple (Datura spp.)
Tree Tobacco (Nicotiana glauca)
- nicotine is the toxic principle
- animals not likely to consume a lethal dose
- symptoms usually resolve within hours
- symptoms include: weak pulse, abdominal irritation, staggering, trembling, salivation and frequent urination
Waterhemlock (Cicuta maculata)
- extremely poisonous, cicutoxin is the toxic principle
- eight species, often found in marshy areas of meadows
- the roots and stalks contain the most poison
- a pea sized bite will kill a human
- symptoms include frothing, nervousness, tremors & convulsions
White Snakeroot (Eupatorium rugosum)
- toxic principle is trematol (an unsaturated alcohol)
- found in wooded areas, stream banks & pastures
- has an accumulative effect
- Trematol is excreted in the milk; humans can be poisoned by the milk of affected animals
- symptoms include: weight loss, trembling, depression, constipation & labored breathing
- affected animals sometimes have acetone odor on their breath
Wild Cherry (Prunus spp.)
Yellow Jessamine (Gelsemium sempervirens)
- contains various alkaloid compounds
- entire plant is toxic
- usually found on stream banks, fencerows or thickets
- usually consumed only when other forage is scarce
- causes weakness, labored breathing, dilated pupils, staggering and convulsions
Yellow Sage (Lantana camara)
- see 'Lantana or Yellow Sage'
Yew (Taxus spp.)
- contains alkaloids
- commonly used as an ornamental shrub
- bark, leaves and seeds are toxic
- highly toxic, but rarely eaten by livestock
- most poisonings occur when trimmings are thrown into pastures
- symptoms include: staggering, diarrhea, lack of coordination, death from cardiac failure
Unique Poisonous Plants can Damage Muscles, Cause Death of Cattle. 2002. LSU AgCenter NEWS. Baton Rouge, LA.
Reducing Livestock Losses to Toxic Plants. A. McGinty & R. Machen. Texas Agricultural Extension Service. College Station, TX. Bulletin B-1499.
Cornell University Poinsonous Plants Infromational Database
Pictures and further listing of toxic plants, as well as more extensive links
Canadian Poisonous Plants Information System
On-line bibliography from the Royal Botanic Gardens in the UK