Toxic Plants

Editor’s Note: For information on these plants and others, contact your local county agricultural agent. Additional information can be obtained by writing to:
U.S. Department of Agriculture
Science and Education Administration
Poisonous Plant Research Laboratory
Logan, Utah84321

Poisonous plants can cause physical malformations, abortions, weight loss, poor health and death. Most noxious plants contain substances that poison by more than one toxic principle. Some of the most powerful poisons are the alkaloids which generally affect the nervous system. The alkaloid is usually distributed throughout he plant and is active whether it is fresh or dry. There are no antidotes for alkaloid poisoning. Some of the common alkaloid-containing range plants are locoweeds, larkspur, groundsel and lupine.

Glycosides are toxins that are particularly dangerous to ruminates. These are compounds composed of a toxic agent combined with a sugar. The toxic agent is harmful when released from the glycoside. Cyanide (HCN, Prussic acid) is the most common toxin in glycosides. Ruminants are more susceptible than monogastrics to poisoning because the microflora promotes cyanide release. Cyanide is generally not retained in plant tissues after drying. Glycoside levels in the plant are often related to freezing, wilting, drought, crushing, and other stressful conditions. Some potential cyanide producers are chokecherry, johnsgrass, and arrowgrass.

Excessive absorption of certain minerals may be dangerous to livestock. Probably the most common in our area is selenium. Certain plants accumulate selenium because it is needed for growth, while others absorb it for no reason. Some plants in the latter category are barley, wheat, and alfalfa. Plans containing more than 5ppm selenium are potentially toxic. Selenium intoxication can occur as acute or chronic poisoning. Some signs of acute poisoning are loss of appetite, depression, polyuria, dyspnea, coma, and death. Chronic poisoning can cause rough hair coat, emaciation, dullness, lameness, and loss of hair. Contact your county agent for information on selenium in your area.

Many plants, both weeds and crops, such as oat and hay, sorghum, corn, Kochia, Russian thistle, and nightshade are examples of plants that accumulate nitrate. Often the type of soil and the form of nitrogen therein influences the amount of nitrate that accumulator plants may contain. Drought conditions and the use of herbicide 2,4-d may cause excessive amounts of nitrate to accumulate. Plants containing more than 1.5% nitrate dry weight may be lethal to livestock. Crops that can accumulate nitrate should be checked for nitrate content. Livestock may be poisoned from eating either harvested or non-harvested forage. In ruminates, nitrates are converted to nitrate and the nitrate causes the production of a type of hemoglobin that cannot carry oxygen. Thus, the effects of nitrate poisoning result largely in oxygen starvation, or in effect, suffocation.

Other toxins are oxalates compounds causing photosensitivity and resinoids. Non-ruminants are more susceptible to oxalate poisoning than ruminants because the large rumen capacity enables the animal to detoxify small amounts of soluble oxalates. Animals that become hypersensitive to light may have swelling about the head, blistering, and a sunburned appearance. Resins are found in milkweeds, marijuana, water hemlock, and chinaberry tree. There are also many plants in which the toxin is unknown.

Each of us has our own unique situation and conditions under which we care for our llamas. Therefore, I would like to give some general rules to follow to help avoid poisoning by toxic plants:

• Know the poisonous plants in your area and conditions under which they are dangerous. Certain species of toxic plants grow earlier in the spring than desirable forage, so animals should not be allowed to graze until there is an adequate amount of good quality forage present. Other plants are poisonous in the fall or only in the fruiting stage of growth.

• Provide adequate salt, Vitamin A, and mineral supplement.

• Provide an adequate quality and amount of forage and water. Most poisonous plants are unpalatable and will be eaten only if other good quality forage is unavailable.

• Do not overgraze pastures as this can encourage growth of toxic plants. Poisonous plants are natural components of ecosystems and may increase in abundance during drought or as range conditions decline.

• Herbicides may be used with certain plants and in appropriate situations. However, keep in mind that herbicides often increase the palatability of toxic plants and therefore, animals should be kept away until all plants are desiccated and removed.

• Purchased hay should be examined for poisonous plants before feeding.

Since many of us are from adjoining states, such as Texas, Colorado, New Mexico, Wyoming, and Nebraska, we have a few poisonous plants in common. Some of these are chokecherry (particularly toxic to ruminants), deathcamas (toxic alkaloids), hemp dogbane (glycoside poison), larkspur (alkaloids), locoweed, milkweed (certain species), Gembel and Shinnery Oak (more than 50% of diet), and Western Waterhemlock (extremely poisonous).

BIBLIOGRAPHY

Plants Poisonous to Livestock in the Western States, United Stated Department of Agriculture, Agriculture Information Bulletin No. 415. This book is excellent but appears to be out of print. You might try writing to the Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402

Poisonous Range Plants of New Mexico, by the Cooperative Extension Service of New Mexico State University and the U.S. Department of Agriculture.

An Annotated Checklist of Poisonous of Injurious Range Plants of New Mexico, by the Cooperative Extension Service of New Mexico State University and the U.S. Department of Agriculture.

Choke Cherry (pictured above)

LEAVES: Alternate, simple, 2"-4" long, tapering or rounded at the base, abruptly pointed tips and sharply serrate margins, bright green above, paler beneath.

TWIGS: Stout, smooth, light brown to reddish brown, with numerous yellowish lenticels. Unlike Fire cherry, the lenticels are not evidently horizontally elongated. Bruised twigs have a disagreeable odor.

FRUIT: A juicy, dark red to black drupe, about ½" in diameter, in open, elongated, drooping clusters. The flavor is harsh and astringent.

BARK: Young trunks shiny, smooth, brownish, peeling off in thin film-like layers exposing the green inner bark. Older trunks dark gray, roughened by shallow fissures.

GENERAL: A fast-growing but short-lived shrub or small tree, rarely exceeding 25'. Found in a variety of open habitats, thickets, roadsides and upland woods throughout the Commonwealth, but more abundant in the western counties. One of the first species to revegetate cleared areas, it is attractive in spring flower and provides food to several dozen species of birds and mammals.