Water hemlock, other plants can kill grazing animals

By Suellen May
Correspondent

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It starts suddenly with muscle tremors and violent convulsions. There is no specific antidote, and death occurs within three hours after a lethal dose: 2 ounces for sheep, 8 ounces for horses and 12 ounces for cattle.

Children have died from sucking on the hollow tubes; adults have made the fatal mistake of confusing it with parsnip and common yampa.

Cicutoxin, found in water hemlock, is the culprit for this poisoning. Water hemlock can be found in wet meadows, riverbanks and alleyways throughout Larimer County.

Poisonous plants present an additional challenge to pasture management, requiring many stewards to identify and treat these plants or at least to remove animals from pastures where poisoning may occur. Perhaps a bigger concern is poisonous plants that may be lurking in hay, completely undetectable by sight, unless it is certified weed-free hay.

"The biggest problem in hay is houndstongue because it's palatable when dry," said Tony Knight, a CSU professor and head of the Clinical Sciences Department.

Houndstongue, named because of the resemblance of the leaves to a hound's outstretched tongue, is avoided by animals when green in a pasture. Poisoning from houndstongue occurs more slowly than water hemlock; 6 percent of a horse's daily intake of food over a two-week period is enough to induce fatal liver disease.

"Another significant problem in hay is horsetail because it can cause blindness and diarrhea in cattle," said Knight.

Horsetail, also called Equisetum or scouringrush, commonly grows in meadows in Larimer County. According to Knight, symptoms such as weight loss begin after a few days of eating horsetail then progress to poor coordination of the hind legs. Horses may die in one to two weeks after they have been unable to get up. If horses suspected of being poisoned by horsetail are treated early enough with thiamine, however, they will likely recover.

Another problem with hay that is not certified weed-free is that it often contains plants of little nutritional value.

"A person might think they are purchasing alfalfa hay but actually it might be 30 to 50 percent poor-quality forbs such as tansy mustard and flixweed that happen to grow in the same environments," said Knight.

These mustards also present the additional hazard of photosensitivity: the lightly pigmented areas of the cattle will become severely sunburned. In some cases, the skin can be peeled off in sheets, providing an environment for infection.

In the spirit of frugality, a Larimer County rancher decided to cut and bale weeds from the roadside--nitrate accumulators such as sunflower, Russian thistle and kochia--and feed them to his cattle. Some of his cattle later died of nitrate poisoning. Not understanding the hazards of weeds in hay, he came to Knight wondering why they had died.

"Trashy grasses such as foxtail barley are also commonly seen in hay," said Knight. "These undesirable grasses have sharp plant parts that cause ulcers in the mouths of horses."

"Although not poisonous, weeds such as leafy spurge and cocklebur are also big problems in Larimer County because they are toxic; these plants won't poison an animal but can cause illness," said Jennifer Gorek, weed specialist for Larimer County. The toxicity of cocklebur is in the seeds and seedlings. Leafy spurge contains a milky latex that is irritating to livestock and people.

One of the best defenses against livestock poisoning is to purchase certified weed-free hay. Hay sold under this program by the Colorado Department of Agriculture is inspected before it is harvested to verify that there are no propagative plant parts of noxious weeds. Purchasing certified hay not only protects the health of livestock but also helps prevent the spread of weeds.

Those wanting more information about noxious weeds may call the Larimer County Weed District at 498-5768. More information on the certified weed-free program, including a list of certified weed-free forage producers by town, is available on the Internet at www.ag.state.co.us/DPI/WeedFreeForage/weedfree.html. Prices vary widely but costs quoted recently averaged $8 a bale.