The potential for animal toxicity and plants is often there for most ecological settings.  However, there are some plants that have an exceptionally poor history related to livestock health.   Plants that are toxic to livestock can be non-selective in their toxicity, meaning they will be toxic to whatever animal comes their way and ingests them, others have some specificity to their toxicity, meaning that they effect just cattle, horses, sheep, etc.  Normally, the toxicity of plants to livestock is not something often witnessed by farmers and ranchers during the 1800s.  It wasn’t until very large ranching operations were developed that events of livestock poisoning became noticeable and were entered into some written document as an important issue ranchers had to come to an understanding about and learn to deal with. 

It is possible that the addition of the railroad to the local landscape had one of the greatest impacts on livestock raising practices in general, sensitizing ranchers to the various other blights animals could have.  Until it became commonplace for cattle to be killed by trains, and for ranchers to begin taking aggressive steps to lay claims to the deaths of these products by filing insurance claims during the late 1800s , the other threats to livestock weren’t that clearly understood.  By the late 1860s or eaerly 1870s, the missing lamb or cow in a flock suddenly was more clearly understood.  It wasn’t just a wolf stalking his prey, or another bad winter, some bad water, or a neighboring rancher laying claim to some of your cattle that was the cause for missing animals, it was now the possibility that this land you had developed presented new risks to livestock health.

There have been a number of books published during the 1800s about livestock disease.  The bulk of these pertain to horses and farriers, but a few of them pertain to sheep and cattle, or even goats and poultry.      Understanding livestock poisoning and the environment is an extremely well-define niche in the field of ever-expanding veterinary science we have today.  Back in the mid-1800s, you were fortunate if you had some background experience and knowledge with forcing a ball of some strong laxative down you horses throat to deal with hairballs and bezoars, or doing the same from the other end to deal with colic and griping, the horses irritability and lack of candor about some pain it is experiencing as you try to get seated in the saddle.    The following are example of livestock poisoning plants that possibly had a relationship with trail migration history and with the establishment of new ranches and farms in the Pacific Northwest.  A couple of examples of important mineral toxicity are noted at the end of this list and brief review as well.

For more on this topic, the following are suggested


Stefferud, Alfred, (Ed.) Animal Diseases.  The Yearbook of Agriculture.  (24th Congress, House Document No. 344.) The United States Department of Agriculture, Washington, D.C.  1956.

Hull, Thomas G.  Diseases Transmitted from Animals to Man. 4ed.  Springfield: Charles C. Thomas, 1955.

Detailed analyses of animal disease, and human disease of animal origin.  The time frame and terminology for these disorders makes it very applicable to Oregon Trail and Pioneer farming history.  Most of the disorders have historical coverage which extend back to Colonial times.   


Kendall, Dr. B.J.  Treatise on the Horse and His Diseases, New Revised Edition.  Dr. J. B. Kendall Co., Enosburg Falls, Vermont. 1942. 

Only a Pamphlet, 80 pages in length.  Covers ca. 150 maladies, with treatments, few recipes, and most of which employing Kendall’s formulas.


Ward T. Huffman, Edward A. Moran, and Wayne Binns. “Poisonous Plants.”  pp. 118-130.  In Stefferud, Alfred, (Ed.) Animal Diseases.  The Yearbook of Agriculture.  (24th Congress, House Document No. 344.) The United States Department of Agriculture, Washington, D.C.  1956.

Plants with a history of livestock poisoning due to ingestion

Oxalate poisoning

Docks (Rumex spp.)

Halogeton (Halogeton glomeratus)

Greasewood (Sarcobatus vermiculatus)

Redroot Pigweed (Amaranthus retroflexus) and other Amaranthus spp.

Astragalus spp.

Princes-plume (Stanleya spp.)

Woody Aster (Xylorhiza parryi)

Tremetol Poisoning (Mild Sickness)–see separate coverage.


      Red Locoweed (Astragalus drummondii)

      White Loco (Oxytropis lamberti)

Researched by James F. Couch, these plants are capable of causing neurological disorders with well defined symptoms.  These are called crazy or loco weeds for a reason. 

Copperweed (Oxytenia acerosa)

Horsebrush (Tetradymia glabrata)

Bracken (Pteridium aquilinum)

Wright’s Eupatorium (Eupatorium wrightii)

So. New Mexico; S.E. Arizona.

Does not have tremetol.

Cattle Lameness

      Tall Fescue (Festuca arundinaceae)–Causes hind limb pain, swelling and paralysis.

Drought/Stress-induced Sorghum poisoning

Johnson Grass and Sudan Grass (Sorghum vulgare)  Native?.  Contains dhurrin, a cyanogenic glycoside which increases considerably in concentration in cases where drought, frost and trampling occur, thus resulting in heightened growth stresses.  Mature plants lose their hydrocyanic potency.  Young plants and secondary growth following heavy feedings increase the concentration of this toxin.  The highest concentration is found in the stubble. 

Poisoning by this form of toxin results in increased respiratory rate, leading to depression, stupor, and convulsions.  Cyanosis and paralysis are indicators that toxicity is setting in.  Lethal cases are irreversible once they begin to show diagnostic signs, and cause fatalities within a few hours, if not much less due to the concentration within the plant.

Select Milkweeds

      Whorled Milkweed (Asclepius subverticillata)

            Extends from Southwest, into Colorado.

      Milkweed (A. labriformis)


Mineral Toxicity

Nitrate Poisoning

Selenium Poisoning

Limestone Disease