Dry Pasture Conditions Pose Extra Risks to Cattle

REGINA - May 22/02 - SNS -- Dry pastures resulting from drought like conditions can create additional risks to cattle when because animals start consuming potentially poisonous plants as normal forages are depleted, says Bryan Doig, livestock agrologist with Saskatchewan Agriculture, Food and Rural Revitalization.

"This increases the risk of poisoning by plants usually avoided by livestock," he says. "Overgrazing, drought and movement of hungry livestock all add to the risk of losses due to poisonous plants. Producers should familiarize themselves with poisonous plants and always inspect new grazing areas for potential problems - this also includes old batteries, fertilizer spills and waste piles of treated grain - before livestock are released."

Tall larkspur, for example, causes a number of cattle deaths each year. It grows from two to six feet tall, has bluish or purple flowers, and is commonly found in aspen forest areas. It is also found in moist areas and on cleared unbroken land.

"A 1,200 pound cow eating eight pounds of larkspur -- 0.7% of body weight -- within a one hour period may die," says Doig. "Research has shown that, as the plants mature, the poisoning agent accumulates in the reproductive parts of the plant."

Poisonous plants common to hillside draws include death camas and chokecherries. Death camas is a slender perennial herb with V-shaped grasslike leaves. It grows from an onion-like bulb to a height of eight to 16 inches, and has many creamy-yellow flowers. It is often confused with wild onion, which has pink flowers and an onion odor. Death camus is most dangerous in the spring as it reaches grazable height before most grasses. About 7.2 lbs of fresh plants are enough to kill a 1,200 pound cow.

Chokecherry plants are most toxic during spring and early summer, but they can become more toxic under dry growing conditions. The poisonous agent is a compound that produces prussic acid (hydrogen cyanide). It only takes about 0.25% of the animal's body weight of fresh or young foliage to cause death (three lbs of plant material ingested by a 1200 pound cow.) The toxicity of the plants varies considerably, but the foliage is toxic at all stages of growth. The buds, flowers and twigs are potentially dangerous.

Poisonous plants common to hillsides and open pasture include early yellow locoweed and narrow-leaved milk-vetch. Locoweed is a low-growing member of the pea family. The plants have a deep taproot, leaves composed of seven to 21 leaflets, and flowers of a pale yellowish color. Livestock usually have to consume large amounts of locoweed over a long period of time before symptoms appear.

Narrow-leaved milk-vetch appears as a semi-erect branched herb that grows one to two feet tall with noticeable cream-colored flowers. Milk-vetches usually indicate that the soil contains high levels of selenium. The plants accumulate inorganic selenium to levels as high as 8,000 parts per million, resulting in selenium toxicity or poisoning in cattle that consume milk-vetch.

Saline and alkaline sloughs are home to seaside arrow-grass. This rush-like herb grows six to 30 inches high. The newer leaves are smooth, thick, shiny, bright green, clumped and un-branched. The flower stalks are taller. The small clustered flowers are greenish in color. Young new leaves are more poisonous than the older parts of the plant. The toxic compound is a glycoside, which forms prussic acid. It is especially poisonous late in the grazing season after a killing frost or in times of drought. As little as 4.4 lbs of plant material can be fatal to a mature cow.

Marshy sloughs, wet meadows and stream banks are home to the deadly western water-hemlock. Water-hemlock is two to six feet tall, and has large, alternate, doubly compound leaves with saw-toothed edges. The leaf veins end near the notches of the leaflets. The tuberous rootstock contains an extremely poisonous yellowish oil. One root can kill a mature cow. Symptoms can occur with 15 minutes to one hour after ingesting a lethal dose.

"It is difficult to treat poisoned cattle. Most often, they are found dead. Producers should learn to recognize poisonous range plants, and try to minimize the availability of those plants to cattle. If the number of poisonous plants is not too large, hand picking or mowing may help to reduce the stands. In some cases, it may be better to fence-off areas that contain large numbers of poisonous plants," says Doig.

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