Livestock specialist Dr. Bruce Carpenter and range specialist Dr. Charles Hart said even normally non-toxic plants can kill livestock under the right circumstances.

"Some desirable forbs are testing as high as 25 percent crude protein," Carpenter said. "This can cause cattle to bloat and die, just like they sometimes do on lush wheat or alfalfa pastures."

He said cattle suffering from bloat may need to be removed from the pasture, given appropriate veterinary treatment, and placed on dry hay to recover.

Locoweed poisoning is also causing problems. Hart said the weed is especially toxic to horses and cattle, though sheep and goats can also be affected.

"Animals usually have to eat the plant for about two months before signs of poisoning appear," said Hart. "Animals can recover from mild cases if removed from the pasture. But permanent brain damage occurs once the animal becomes ‘locoed.' Signs include excessive excitability, especially in horses, low head carriage, trembling, difficulty eating and drinking, abortion, or weak or deformed offspring.

"Often, once animals begin to eat the plant, they continue to seek it out. So about the only practical way to remedy the problem is to remove the affected animal and place it in a pasture with little or no locoweed."

Hart said Peavine or Emory Loco is an annual variety that grows mainly in and around limestone hills. Its toxin and poisoning signs are different from other species of locoweed, though the treatment for affected animals is the same. The plant causes coordination problems in the animal's hind legs.

Tansy mustard is another plant causing problems across much of its range, Hart said. Normally, when consumption is moderate, tansy mustard is a desirable, nutritious forage. But this year is an exception.

"It's causing problems in two ways," said Carpenter. "Tansy mustard contains an unidentified chemical that causes tongue paralysis and blindness in cattle. Affected cattle often begin ‘head-pressing.' They stand and press their heads against immobile objects. Because they are blind, they don't eat or drink so death occurs through dehydration and rumen impaction. Most will recover though if removed from the affected pasture, re-hydrated and fed.

Hart said indirect evidence indicates that tansy mustard is also causing sudden death via nitrate poisoning.

"To date, there have been several documented cases of nitrate poisoning in cattle across the region," Hart said. "We've got other weeds that will do the same thing, but they are not up and growing yet. Tansy mustard is. We know the plant can accumulate nitrates when warm days produce rapid growth that is suddenly interrupted by a freeze, or even just cloudy and cold weather; which we've had a lot of lately.

"People are often confused between tansy mustard and its more robust cousin - London rocket mustard. As far as anyone knows, London rocket is not poisonous. Tansy mustard grows to 6 inches to 2 feet, with deeply divided frilly or lacy leaves, often with a gray-green color. This is the best way to tell it apart from London rocket, which has a much larger, lobed (vs. lacy), deep green (vs. gray-green) leaf, and often grows from 6 inches to 3 or 4 feet in height. London rocket mustard is growing all across West Texas this spring."

But both specialists said the presence of poisonous plants does not necessarily mean a poisoning will occur.

"Keep an eye on your livestock," said Carpenter. "And chances are you'll have no problems."

To learn more about toxic plants, visit: http://texnat.tamu.edu/cmplants/toxic/index.htm .

Note: If no author is given, the source is cited instead.

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