Plants Poisonous to Livestock on Western Rangelands

August 29, 2014 Print Friendly and PDF

Written by Mindy Pratt, Utah State University Extension

Poisonous plants are a major cause of economic loss to the livestock industry. Each year poisonous plants adversely affect 3 to 5 percent of the cattle, sheep, and horses that graze western rangelands.

Colorado Rubberweed or Pingue (Hymenoxys richardsonii), courtesy of Dr. James Bowns


Causes of Livestock Loss

Livestock losses can be heavy if:

  • Animals graze infested rangelands when plants are most toxic.
  • Animals are driven, trailed through, or unloaded from trucks onto rangeland or pasture areas infested with poisonous plants.
  • Animals are not watered regularly or are allowed to become hungry, making them more likely to eat lethal quantities of poisonous plants.
  • Animals are allowed to graze in heavy stands of plants that are highly poisonous.
  • Animals are grazed on rangelands early in the spring when there is no other vegetation except poisonous plants.


There are no known treatments for animals poisoned by most poisonous plants. Where treatment is available, affected animals are usually in remote places and cannot be reached until it is too late to apply the treatment. When they have recovered enough to be handled, treatment should consist primarily of symptomatic treatment except where a specific treatment is known.


Preventing animals from consuming too much of a poisonous plant in the first place is the best way to avoid livestock losses to poisonous plants. However, livestock grazing on rangeland generally cover large areas with a diverse array of plants. It is difficult, if not impossible, to prevent livestock from coming into contact with poisonous plants; however, following a few guidelines can minimize the likelihood of a severe loss to poisonous plants.

To protect your animals from poisoning:

  • Learn to identify the poisonous plants that grow on your rangeland.
  • Learn the conditions under which these plants can be dangerous to your livestock.
  • Develop a grazing plan to improve your rangeland and prevent poisoning of your livestock by plants. Graze your rangelands at the proper time, and do not overgraze them.
  • Do not allow animals that have been under stress or that are overly hungry to graze in areas infested with poisonous plants.
  • Provide adequate water for your livestock.
  • Be especially careful when grazing newly introduced livestock on your rangeland.
  • Provide adequate salt and other supplements as needed.
  • Control poisonous plants where feasible.
  • If your animals get sick, consult your veterinarian to ensure proper diagnosis and treatment. If a poisonous plant is involved, identification of the plant is essential for any corrective action.

Poisonous Plants List

Plants poisonous to livestock on western rangelands include:

  • Arrowgrass (Triglochin maritima and T. palustris)
  • Bitter Rubberweed (Hymenoxys oderata)
  • Broom Snakeweed (Gutierrezia sarothrae)
  • Chokecherry (Prunus virginiana)
  • Cocklebur (Xanthium strumarium)
  • Colorado Rubberweed (Hymenoxys richardsonii)
  • Copperweed (Oxytenia acerosa)
  • Deathcamas (Zigadenus spp.)
  • Desert Baileya (Baileya multiradiata)
  • Gray Horsebrush (Tetradymia canescens)
  • Greasewood (Sarcobatus vermiculatus)
  • Halogeton (Halogeton glomeratus)
  • Hemp Dogbane (Apocynum cannabinum)
  • Horsetail (Equisetum spp.)
  • Inkweed (Drymaria pachyphylla)
  • Low Larkspur (Delphinium spp.)
  • Littleleaf Horsebrush (Tetradymia glabrata)
  • Lupine (Lupinus spp.)
  • Milkvetch (Astragalus spp.)
  • Milkweed (Asclepias spp.)
  • Oak (Quercus spp.)
  • Poison Hemlock (Conium maculatum)
  • Ponderosa Pine (Pinus ponderosa)
  • Rayless Goldenrod (Isocoma pluriflora)
  • Riddell Groundsel (Senecio riddellii)
  • St. Johnswort (Hypericum perforatum)
  • Sneezeweed (Hymenoxys hoopesii)
  • Spring Parsley (Cymopterus ibapensis)
  • Tall Larkspur (Delphinium spp.)
  • Tansy Ragwort (Senecio jacobaea)
  • Threadleaf Groundsel (Senecio longilobus)
  • Threadleaf Snakeweed (Gutierrezia microcephala)
  • Waterhemlock (Cicuta douglasii and C. maculata)
  • Western Brackenfern (Pteridium aquilinum)
  • Western False Hellebore (Veratrum californicum)

Feature photo: dwolfgra / Foter / Creative Commons Attribution 2.0 Generic (CC BY 2.0)

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This work is supported by the USDA National Institute of Food and Agriculture, New Technologies for Ag Extension project.