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Drought Related Livestock Poisoning by Weeds

Photo courtesy of the Walsh County Soil Conservation District

An algae bloom in Walsh County has tested positive for toxic cyanobacteria production. (Photo courtesy of the Walsh County Soil Conservation District)

Cyanobacteria, also known as blue-breen algae, can produce toxins that are harmful to livestock

Poisonous weed identification and recognizing common poisoning symptoms is important to determine the possible cause of livestock illness or death.

July 2017

Richard ZollingerWeed Specialist

A number of livestock deaths are reported each year from unknown causes. Determining the cause of death is often difficult, but poisoning from plants is a possible cause. Several weed species commonly found in North Dakota can produce toxins or poisons in large enough quantity to kill livestock that feed on the plant. Poisoning most often occurs in overgrazed areas or in dry years when desirable forage is limited. Livestock may graze on poisonous plants they normally would not eat if more palatable forages were available in adequate supply.

Some plants accumulate toxins only during certain growth stages or when growing under stress. Hydrocyanic acid (sometimes called prussic acid) is an example of a toxin produced by some weeds as well as some crops when plants are stressed. Therefore, the chance for livestock poisoning may be increased when hot, dry weather conditions persist. The following is a list and description of various plant species which could poison livestock and humans.

Water hemlock: Water hemlock is a large plant which grows 3 to 5 feet tall with smooth green or purplish stems. The leaves are repeatedly divided into three parts, and the flowers are white, very small, and grow in umbrella-like flat clusters which appear in July and August. Water hemlock also has a tuber-like root that smells like parsnips and is the plant part that has the highest concentration of toxin. Water hemlock poses a threat to humans as well as livestock because it can be mistaken for common parsnip. The toxin in water hemlock is one of the most dangerous poisons produced in plants and can cause acute distress, convulsions, and death within one or two hours of consumption. Water hemlock occurs most commonly with moist soils in eastern North Dakota.

Silvery and false lupine: Lupines occur on the range in western North Dakota. Both plants are perennial species which grow 1 to 2 feet tall, have multiple leaflets attached at one point, pea-shaped flowers, and flat seed pods 1 to 2 inches long. The seeds and pods are especially poisonous and sheep are most often affected. Lupine poisoning can result in frothing, trembling, excitement, and butting into other animals and objects.

Camas: Camas is a lily or onion-like perennial plant which grows from an elongated white bulb to a height of 1 to 2.5 feet tall with small white flowers. Camas poisoning results in rapid breathing, excess salivation, convulsions, and possible death. Camas is found throughout the state and is most common in moist grasslands or on sandy slopes.

Locoweed and Crazyweed: Locoweed is the most abundant poisonous plant in North Dakota and can be found throughout the state, although it is most prevalent west of the Missouri River. Crazyweed is very similar to locoweed in appearance. Locoweed is a stemless, thickrooted perennial with seven to ten pairs of leaflets on a compound leaf about six inches long. The flower stems are upright and generally taller than the leaves with violet to purple, or white flowers. Pointed seed pods, about 0.5 inches long and hairy, develop at the end of the flower stalk. Locoweed and crazyweed symptoms include weakness, loss of coordination, and lack of muscular control. Animals may acquire a taste for locoweed and consume large quantities. Locoweed poisoning is uncommon and can be cured by removing the animals from the infested area.

Larkspur: Larkspur is an erect perennial, 1 to 1.5 feet tall, with leaves divided into narrow segments growing near the ground. Bright blue, lavender, or white flowers develop on a terminal spike in May. Smooth brown pods form in groups of three, and split along the inner edge. Larkspur poisoning results in staggering, repeated falling, and respiratory paralysis, mainly in cattle and rarely in sheep or horses.

Arrowgrass: Arrowgrass is a rush-like plant with thick, narrow leaves and small purple flowers in a slender spike on a stalk 1 to 2 feet tall. Arrowgrass occurs throughout North Dakota in marshy soils and on wet alkaline flats. The toxic substance in arrowgrass is hydrocyanic acid which becomes more concentrated when plants are growing under stress. Hydrocyanic acid poisoning results in abnormal breathing, trembling, convulsions, and death.

Cocklebur: Cocklebur is a broadleaved annual weed 2 to 4 feet tall with rough textured leaves and stems. Burs, 0.5 to 0.75 inches long, develop in clusters near the base of the leaves. The young seedlings are most poisonous and most often eaten by hogs. Older plants are less palatable and less poisonous. Cocklebur poisoning causes weakness, rapid breathing, convulsions, and death. Cocklebur occurs mainly around water and on flood plains, and is most common is the southeastern part of North Dakota.

Sneezeweed: Sneezeweed is a leafy perennial plant which grows 1 to 2 feet high with yellow sunflower-like heads, 0.75 inch wide, that appear in August. Sneezeweed grows in low moist areas and is not common in North Dakota. Sneezeweed poisoning is most common in sheep and causes vomiting, coughing, and bloating.

Horsetail: Horsetail is a perennial species with green jointed stems and no leaves or flowers. Horsetail is also called scouring rush and generally occurs along the edges of streams and in marshy areas. Poisoning results in loss of vigor, trembling, and eventually paralysis.

Chokecherry: Chokecherry is a common shrub or tree found throughout the state where moisture is plentiful. The leaves of chokecherry can produce hydrocyanic acid and cause abnormal breathing, trembling, convulsions, and death.

Unexplained livestock illness or death is not always due to poisonous weeds. Crops can also produce toxins under certain conditions. Sudangrass and green flax straw may produce hydrocyanic acid after clipping or a light frost. In addition, livestock can become ill due to a nutrient imbalance, such as nitrate or selenium poisoning. Toxic nitrate levels commonly occur in many plants when growing under stressed conditions such as extreme drought. Lightning, venomous bites, or consumption of other toxic substances are other possible reasons for unexpected livestock deaths. However, recognition of common poisoning symptoms and identification of poisonous weeds is important to determine the possible cause of livestock illness or death.