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Toxic encounters with range plants.

In summer, purplish-blue lark-spur blossoms decorate mountain hillsides and meadows in the western United States. But, beautiful as they are, these plants can be deadly when cattle feed on their foliage.

Larkspur, like pine needles, locoweed, lupine, and a host of other plants found in western pastures, contains toxins that can poison unwitting, hungry livestock.

When pregnant animals graze certain poisonous plants, the consequences can be especially gruesome - an offspring with twisted, deformed legs caused by toxins in lupine, or the bizarre, one-eyed lamb that can result when ewes eat false hellebore, a plant in the lily family.

Western ranchers suffer losses to the tune of $340 million each year because of poisonous plants, according to Lynn F. James, research leader at the ARS Poisonous Plants Research Laboratory.

Located in Logan, Utah, about a 2-hour drive north of Salt Lake City, the laboratory is the only one of its kind in the world. James and his team of scientists work to identify toxic plants and their poisons, describe their effects, and develop new ways to prevent poisonings.

The loss figure related to poisonings includes only deaths and reproductive disturbances. But there are other, less tangible costs, such as reduced weight gains in ill animals. Other indirect expenses include fencing pastures, herding cattle to steer them away from dangerous plants, and poisonous plant eradication efforts.

Hundreds of plants growing on western ranges can harm grazing livestock. Some have killed humans, too; the ancient Greeks executed the philosopher Socrates with a lethal tea brewed from hemlock. Today, people sometimes eat the bulbs of a grassy perennial called deathcamas, mistaking them for edible roots.

In terms of cattle losses, however, some of the worst offenders are larkspur, ponderosa pine, and locoweed.

U.S. ranchers in the intermountain West lose more cattle to larkspur than to any other poisonous plant. Cows like to eat the plants with spur-shaped flowers, which grow up to 6 feet tall in dense, abundant clumps in mountain pastures throughout the West.

Chemist Gary D. Manners, with the ARS Plant Protection Research Unit in Albany, California, has identified at least 15 different toxins, compounds known as alkaloids, in a single larkspur plant.

In cooperation with Logan animal scientist Kip E. Panter, he is trying to pinpoint which alkaloid is responsible for the plant's nasty effects on cattle.

Once Manners identifies the toxin, he and Logan range scientist Michael H. Ralphs will determine whether the toxin's concentration in the plant changes in response to variables like temperature, moisture, or shade.

Trained Cows and Peer Pressure

With that information, they may be able to predict when the risk of poisoning is greatest. Logan scientists can then help ranchers work out the safest grazing strategies.

Tactics to stop larkspur poisonings take a variety of forms. One approach is simply killing the plants with herbicides. Ralphs, along with Utah State University scientists, has studied several promising chemicals, including metsulfuron, that work at very low concentrations on young larkspur.

"Herbicides may be useful to reduce dense patches of larkspur that cause poisonings year after year," says Ralphs. Widespread use, however, isn't practical because of the expense and because the plants often grow on rough, mountainous terrain that's not easily accessible.

If snuffing out the plants doesn't work, an alternative may be training cattle to avoid the attractive flowers.

Ralphs has tried a novel strategy known as aversive conditioning. He fed the cows small amounts of fresh larkspur and then dosed them - through a stomach pump - with lithium chloride, a chemical that nauseates them. The cattle associated the taste of larkspur with the illness and subsequently refused to eat it.

Initially, the experiment was successful. Animals staunchly avoided the plants in meadows. But the trained cows reverted to eating larkspur when they were placed in a field with untrained cohorts who were happily devouring the stuff.

Continued research will show if the aversion can be strengthened to overcome the influence of their peers.

If a cow does gobble a few mouthfuls of larkspur, is there any other possible way to thwart the toxin? Maybe, says animal scientist James A. Pfister of the Logan lab.

Pfister is investigating another potential strategy, a miniature pump that could be surgically implanted under a cow's skin. The pumps would release a protective compound - as yet unidentified - that would counteract the larkspur poison.

The pump is about the size of a man's little finger, large enough to slowly release drugs for about 28 days. Eventually, researchers might be able to fashion smaller pumps or pellets that could be implanted under the skin, similar to the implants now used in cattle to slowly release growth hormones.

"Larkspur is dangerous to cattle for about 6 weeks during summer, so during that time the pumps could be used to protect cattle," says Pfister.

He's working with scientists at Colorado State University to identify a protective compound.

"Larkspur toxins seem to interfere with chemical compounds found at the nerve junctions. We're looking for something that could counteract that effect," says Pfister.

Like larkspur, ponderosa pines are also abundant in the West. If pregnant cows eat the long, soft needles of the ponderosa pine during the final trimester of pregnancy, they're likely to abort their calves.

"Even if the cows don't abort, they'll often have premature, smaller calves that aren't as healthy as normal calves," says James. "Pine needles may cause losses totaling $20 million each year."

Robert Short, an ARS physiologist based in Miles City, Montana, works with the Logan scientists in efforts to identify the physiological mechanisms responsible for abortions. Their earlier studies found changes in levels of progesterone, a hormone important in pregnancy, in cows that ate pine needles.

Affected cows also have a tendency to retain their placentas instead of expelling them after the calf is born. Infections can result, and the cow may take longer than usual to rebreed.

Researchers aren't sure why cows eat the needles, which are chockfull of bitter chemicals. Pfister found, however, that nonpregnant animals eat as many pine needles as their pregnant sisters.

Other harmful plant toxins include alkaloid compounds found in lupines (members of the pea family), poison-hemlock, and various tobacco species, as well as larkspur. These can cause skeletal deformities such as cleft palate.

At the Logan lab, Kip Panter uses ultrasound imaging, common in human medical diagnosis, to observe developing animals whose mothers have eaten toxic plants. His aim is to learn exactly how and when the toxins harm fetuses.

"We've found that some of the alkaloid toxins actually sedate the growing fetus and keep it from kicking and stretching normally while it's in the uterus," says Panter. Consequently, calves' spines and legs may be crooked, instead of supple and flexible. In some herds, as many as 30 percent of calves suffer these deformities.

The ultrasound studies revealed that lupine and poison-hemlock are most dangerous when the pregnant cows graze them between the 30th and 70th day of gestation. Continued studies should narrow this "toxic window" even more.

Lynn F. James, Kip E. Panter, James A. Pfister, and Michael H. Ralphs are at the USDA-ARS Poisonous Plant Research Laboratory, 1150 E. 14th N., Logan, UT 84321. Phone (801) 752-2941. Gary D. Manners is at the USDA-ARS Plant Protection Research Unit, 800 Buchanan, Albany, CA 94710. Phone (510) 559-5813. Robert Short is at the USDA-ARS Range and Livestock Research Unit, Rte. 1, Box 2021, Miles City, MT 59301. Phone (406) 232-4970.
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Title Annotation:Agricultural Research Service's Poisonous Plants Research Laboratory
Author:Corliss, Julie
Publication:Agricultural Research
Date:Dec 1, 1991
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