1. Important Poisonous Plants of the Western United States
Chemistry: Characterize, quantify & purify plant toxins, ELISA development
Plant Biochemistry & Physiology: Genetic & environmental influences on toxins; chemical phenology; chemotaxonomy; toxin synthesis
Vet Sci & Toxicology: Pathology (diagnosis/ prognosis), toxicokinetics, mechanism of action
Core Solutions
An interdisciplinary approach used by the Poisonous Plants Research Laboratory in Logan UT. The mission of the Poisonous Plant Research Laboratory is to identify poisonous plants and their toxins, determine how the plants poison animals, develop diagnostic and prognostic procedures, identify the conditions under which poisoning occurs, and develop management strategies and treatments for ranchers to reduce livestock losses. Reference for this lesson is available as a pdf. and can be downloaded as companion material in the rangeland teaching clearinghouse.
Animal & Range Science: Effects of toxins on reproduction, animal physiology, behavior & nutrition; genetics; plant population ecology; consumption of toxic plants by grazing animals

2. Losses to Toxic Plants Death Impaired Gains Abortions Birth Defects
Indirect Losses:
Vet costs
Change in management
Increased risk
Decreased land value
Total losses to U.S. livestock industry exceed $300 million annually.
3-5 percent of all livestock that graze on western rangelands are adversely affected by toxic plants.
USDA -ARS
USDA -ARS
This set of 25 slides will show and discuss some of the more economically important toxic plants according to the USDA-ARS Poisonous Plant Research Laboratory. It will take approximately 150 minutes to cover the material in this set of slides and another 35 minutes to administer and review the quiz in the noteguide.
USDA -ARS
USDA -ARS

3. The Dose Makes the Poison
“All substances are poisons; there is none which is not a poison. The right dose differentiates a poison from a remedy.” Paracelsus ( )
LD50 – Lethal dose, the amount of toxin needed to kill 50% of test population, usually expressed in mg/kg
Active ingredient/toxin
Alkaloid-accumulating plants
Larkspur, locoweed, lupine
Nitrate-accumulating plants
Milkvetch, stressed annual crops such as oat hay, corn, sudangrass
Selenium-accumulating plants
Asters, princess plume, milkvetch
Cyanide toxicity
Chokecherry, arrow grass, service berry
The importance of knowing the active ingredient or toxin helps in determining management strategies and possible remedies.

4. Larkspur (Delphinium spp.)
Divided into three categories
Tall - Found in moist mountain sites 6,000-10,000 feet elevation in the western U.S. grows 3-6 feet tall. (D. barbeyu, D. occidentale, D. glaucescens, D. glaucum, and D. ramosum)
Low - Grows early in spring on foothill and mountain ranges 3,000-6,000 feet elevation 6-30 inches tall. With adequate moisture may persist for 6-8 weeks. (D. nuttallianum, D. andersonii, D. scaposum, and D. bicolor)
Plains – Problem on high plains of Colorado and Wyoming, 2-3 feet tall. (D. geyeri)
Responsible for $6-10 million in losses annually
Marsh (1913) stated that larkspurs kill more cattle on western ranges than any other plant.
Currently today larkspur is still the most toxic plant to cattle on western rangelands. However the plant that kills the most livestock in the U.S. is alfalfa.

5. Identifying larkspurs
Upper sepals extend into a spur
Petals bluish-purple
Leaves alternate, simple,
petiolate, blades palmately divided,
divisions 3-9, divisions cleft, (petiole)
Fruit pod-like follicle
when dry looks like a
Jester hat
USDA -ARS
It would be ideal to have some plant mounts to pass around the class to show the key identification characteristics of all the plants discussed in this set of slides.
USDA -ARS
USDA -ARS

6. Clinical signs of larkspur poisoning
The relative toxicity and concentration of individual alkaloids varies among species of larkspur. The toxic alkaloids cause death by neuromuscular paralysis.
Weakness and staggering gait; animal may fall suddenly
Salivation
Muscular twitching
Difficulty breathing – rapid and shallow
Nausea and vomiting
Rapid irregular pulse
Death occurs from respiratory paralysis and/or bloat
Excitement intensifies all signs of poisoning
The cholinergic drug “Neostigmine “(0.02mg/kg intermuscular) has been successfully used to reverse clinical larkspur intoxication. Drug therapy is not practical in most range situations, catching and constraining the animal will aggravate the symptoms and cause death.
USDA -ARS

7. Factors that influence ingestion and toxicity to cattle
Time of year and stage of growth
Cattle eat less larkspur during
drought
Amount of larkspur present
Current vegetation composition
Some cattle breeds tend to
be more tolerant than others
Some species of larkspur are
more toxic than others
How many consecutive days larkspur is consumed
The understanding of the toxic window has lead to cattle managers deferring grazing in high larkspur concentrated areas until after flowering.
J.A. Pfister

8. Sheep resistance to larkspur
Sheep must eat 4-5 times more larkspur to show symptoms of poisoning compared to cattle.
Research has shown sheep have an affinity to bind methyllycaconitine (MLA) at neuromuscular junction. Thus reducing the effect of MLA on muscular paralysis.
Methyllycaconitine is most common toxic alkaloid in larkspur (LD50 is about 4 mg/kg in mice)
Symptoms of poisoning can be seen in sheep if they are herded or excited.
Kay Benson

9. Management of larkspur
Avoid toxic window
Create larkspur free areas if possible
Herbicides – 1oz Metsulfuron-methyl tank mixed with 1pint 2,4-D ester formulation sprayed in vegetative stage has resulted in 90% control. Dead plants are palatable and potentially toxic-no grazing for one year.
Graze sheep before cattle
Consider aversive conditioning
Use rider to redistribute animals
Do not excite animals it will exasperate the toxicity
Low larkspur can be controlled with 2-4-D. Tall larkspur can be controlled with picloram. Both these herbicides will damage other broadleaf forbs and shrubs as well.

10. Lupine (Lupinus spp.)
Five poisonous species (Lupinus sericeus), (L. caudatus), (L. leucophyllus), (L. argenteus), and (L. formosus)
Species are not uniform in alkaloid composition
Not all species contain teratogenic alkaloids
Toxic species are toxic entire growing season, younger plants are more toxic than older plants.
Lupine is a native legume that fixes nitrogen. It will form a seed pod and has a very characteristic palmate leaf.
USDA -ARS
USDA -ARS

11. Lupine induced crooked–calf syndrome
Teratogenic alkaloids may cause death to sheep and cattle depending on the stage of growth and amount consumed.
In cattle if consumed during day of gestation malformations such as cleft palate, torticollis and kyphosis may occur in the calf.
Torticollis
Kyphosis
Cleft palate
Lupine is very toxic to sheep and typically causes birth malformations in cattle.
USDA -ARS
USDA -ARS
USDA -ARS

12. Lupine management
Grazing occurs as a function of palatability and availability compared to other vegetation present.
Cattle with higher Body Condition Scores (BCS) tend to consume less lupine than cows of lower BCS.
Graze steers or bulls in pastures with teratogenic lupine species.
Shift breeding dates to avoid toxic window for mother cows.
No known treatment for lupine poisoning.
USDA -ARS

13. Locoweed (Astragalus spp.) (Oxytropis spp.)
Astragalus and Oxytropis species that contain the toxin swainsonine.
Fungal endophyte isolated from toxic locoweeds that produce swainsonine.
Rank order of toxicity, garbancillo (A.wootoni) > wooly loco (A. mollissimus), = spotted loco (A. lentiginosus) > white point loco (O. sericea)
Locoweeds tend to grow cyclic, because many are short lived perennials or annuals depending on precipitation patterns.
USDA -ARS

14. Locoweed production cycles
Oxytropis, generally are long lived perennial plants.
Green locoweed leaves are selected by cattle, horses, and sheep in grazing trials.
Astragalus, generally are cyclical based on fall and spring precipitation.
Many locoweeds begin growth before cool season grasses.
Locoweeds remain palatable late in the fall after warm season grasses have gone dormant.
Palatability is a function of other available forage.
Healthy rangeland conditions with perennial bunchgrasses will reduce the consumption of locoweeds, therefore reducing the occurrence of poisoning.
White point loco
Spotted loco
USDA -ARS
USDA -ARS

15. Locoweed losses
Spanish word “loco” means (crazy), which describes the behavior of poisoned animals.
Abnormal behavior such as extreme nervousness, inability to eat and drink.
Abortions and reduced libido
Wasting type of condition, dull eyes and dry hair coat.
There is no effective treatment for locoweed poisoning.
USDA -ARS

16. Ponderosa pine (Pinus ponderosa)
Abortions in cattle from pine needles
Affects only cattle in mid to late gestation
Weather forces cattle to take shelter under ponderosa pine trees
Low BCS cows eat more needles than higher BCS cows
Dead calves and retained placenta
Prevent access to pine trees during last trimester of pregnancy
Keep cows out of pastures with ponderosa pine trees during late gestation.
USDA -ARS
USDA -ARS

17. Broom snakeweed (Gutierrezia sarothrae) Threadleaf snakeweed (G
Broom snakeweed (Gutierrezia sarothrae) Threadleaf snakeweed (G. microcephala)
Toxins probably terpenes, similar to pine needle abortion
More toxic on sandy soils than on limestone soils
Abortions and retained placenta
Another weather influence consumption of a plant that is normally not very palatable.
USDA -ARS

18. False hellebore (Veratrum californicum)
Sometimes called wild corn or cow cabbage
Grows on moist open meadows and hillsides at 6,000-11,000 feet elevation
Toxicity decreases as plant matures
Causes monkey-faced lambs if ewe consumes it on 14th day of gestation
Remember sheep are short day breeders, so false hellebore should not be present in fall breeding pastures.
USDA -ARS
USDA -ARS

19. Death camas (Zigadenus species)
Contains toxic steroidal alkaloids
Entire plant is toxic and dangerous at all times
Begins growth early in the spring
Causes salivation, nausea, vomiting, staggering, convulsions and death
Sheep are most susceptible but cattle, horses and humans have been poisoned
Can be confused with wild onion. Grows at high elevations and is usually early to green-up.
Sheep carcasses
USDA -ARS
USDA -ARS

20. Yews (Taxus spp.) Shrubs used for landscaping
Most poisoning occur from feeding livestock trimmings
Most toxic of all poisonous plants
Cardiovascular toxin
Very small amount of plant material needed to be fatal
Be careful with some of the ornamental shrubs grown in the west. Do not feed trimmings to livestock.
Cattle fed clipping
Japanese yew
USDA -ARS

21. Halogeton (Halogeton glomeratus)
Invasive annual plant, grows in disturbed area such as road sides and trails
Thrives in saline soils
Seed bank is viable up to 20 years
Toxic substance is sodium oxalate
Becomes more toxic as it matures
Usually a problem on winter range allotments.
1200 dead sheep USDA-ARS

22. Nitrate accumulating plants
Rapid growing annual crops/weeds (oat hay, corn, kochia, pigweed and nightshade) accumulate nitrates
Drought conditions may cause nitrate accumulation
Nitrates are converted to nitrite by rumen microbes
Nitrite causes the production of methemoglobin
Methemoglobin can not carry oxygen resulting in blue coloration of membranes around mouth and eyes
If not fatal may cause abortion
Test feed and do not feed if concentrations of KNO3 is greater than 1.5% on a dry weight basis
Can diluted with low-nitrate forage
Some aftermath feeds can be high in nitrates as well such as corn stalks and wheat straw. Be aware nitrate poisoning can be caused by high levels of nitrogen in water.

23. Selenium accumulating plants
Plants containing more than 5 ppm selenium are potentially toxic
Primary accumulator group includes milkvetchs (Astragalus spp), woody aster (Machaeranthera section Xylorrhiza) and princes plume (Stanleya pinnata)
Secondary accumulator group includes saltbush (Atriplex spp), Indian paintbrush (Castilleja spp),and gumweed (Grindelia spp)
Nonaccumulator group includes grasses such as western wheatgrass and small grains most problematic because they are readily consumed by livestock
Sheep do not show the typical signs of poisoning, they are more susceptible to sudden death.

24. Symptoms of selenium toxicity
Acute poisoning
Abnormal posture
Unsteady gate
Diarrhea
Increased pulse and respiration rate
Death
Chronic poisoning
Dullness
Rough hair coat
Loss of long hair
Hooves may become overgrown
Lameness
Use of soil maps may show pastures that may lend themselves to selenium accumulation in plants.

25. Cyanide toxicity
Cyanogenic glycosides are converted to cyanogenic acid by rumen microbes resulting in poisoning
Young plant tissue highest in HCN
Frost and drought can increase HCN concentration
Herbicides may increase HCN concentration
Plants that are cyanide toxic
Johnson grass (Sorghum halapense)
Sudan grass (Sorghum vulgare)
Chokecherry (Prunus virginiana)
Service berry (Amelanchier alnifolia)
Arrow grass (Triglochin spp.)
Death is usually very rapid. Chokecherry leaves are the toxic part of the plant.