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Toxic Plants Cause Wide Array
Of Problems For Livestock

By Colleen Schreiber

(Editor's note: This is the fourth and final installment in a series of articles about toxic plants.)

AUSTIN ó The last category of toxic plants discussed at the recent Texas and Southwestern Cattle Raisers Association School for Successful Ranching, held in conjunction with the organization's annual convention, was what was dubbed the "Other" category. This group of plants causes a variety of different and sometimes unique symptoms in livestock that graze or browse them.

Drs. John Reagor and Charlie Hart discussed the various plants in this category, including a short description of the plant, how to identify it, how and where it grows, and when it is most poisonous. They also identified the toxic agent, if known, the classic symptoms of poisoning, and which animals it tends to affect.

The first plants discussed were the oaks. Oak poisoning is widespread across the state. The toxic agent found in oaks is gallotannin. It is found in high concentrations in the buds, flowers, young stems and acorns, but the mature leaves are not toxic.

With tree oaks, the problem generally is with acorns. Acorn poisoning occurs mainly in the spring, and Reagor said he expects to see cases in his lab any time. He added that he sees more problems when there is a big acorn crop and the acorns are just beginning to sprout.

Tree oaks such as post oak can also be a problem if the young buds and immature leaves are knocked off during a severe rain or hailstorm.

Shinnery, a low-growing shrub oak, he said, is more of a problem in the sandier soils of West Texas, where it is more common. The problem occurs at bud break and with new growth, mainly because thatís when it is fairly succulent and palatable.

The clinical signs of oak poisoning are not dramatic, Reagor said.

"Cows are a little depressed. They stand off by themselves. Sometimes you might see a little swelling above the udder between the hind legs. If you notice bloody froth coming from the animalís mouth, thatís because the animal's capillaries are very fragile. The animal might also have a little diarrhea. The cow will die in two or three days and thereís really not much you can do in the way of treatment."

The toxic agent can cause liver failure in horses and dogs. Sheep and goats are only poisoned when oak makes up the majority of their diet.

In heavy shinnery country a preventative type feed can be fed to lesson the chances of poisoning. A feed made up of 10 percent hydrated lime, six percent fat, 30 percent alfalfa and 54 percent cottonseed meal fed at four pounds per head per day works well if fed before bud set in the spring.

"If you have a cow that is already showing renal failure, thereís no need to feed this preventative feed because the toxin has already done its damage," he added.

Shinnery can be controlled by using Spike 20P at a rate of three-quarters of a pound of active ingredient per acre.

There are a variety of locoweeds, but not all are poisonous. Hart told listeners that to properly identify a locoweed requires the flowers, fruits and leaves. One of the distinguishing characteristics of woolly loco is an alternating leaf pattern. Leaves are woolly, as the name would indicate.

Woolly loco is one of our more toxic plants, Reagor said, but it takes a lot of loco to cause problems. It is toxic to cattle, sheep, goats and particularly horses. A horse only has to eat 30 to 40 percent of its body weight to be lethal, while a cow has to eat more than 100 percent of its body weight for it to be lethal over a period of time.
The toxic agent, swainsonine, causes damage to the liver, digestive organs, the placenta and testes, but the one organ to which it causes the most damage, he noted, is the brain. Most of the other organs repair themselves.

An animal that has loco poisoning carries its head a little lower than normal, has a vacant stare, trembling of the head and difficulty eating and drinking.

The biggest dollar losses occur in the western part of the state and are due mostly to abortions. Reagor said that in a bad loco year it's not unusual to have a 40 to 50 percent abortion rate. Abortions may occur even though the animal has not yet eaten enough loco to show central nervous system signs.

The plant is toxic when it is green and growing as well as when it's dead. Reagor warned listeners to be careful of introducing outside cattle to areas where there is a lot of woolly loco. Native cattle will usually do fine.

It was once thought that loco is addictive. Leading authorities have since determined that it is not addictive, but that consumption is a learned response.

"If you see one animal eating loco, remove that one from the herd so the others donít watch that one and start eating it as well," Reagor advised. "If they havenít learned to eat the plant, then those animals can usually live in a pasture that has high woolly loco problems."

One management tool is to use heavier stock densities in pastures that have loco problems. That way animals are less likely to eat enough to cause toxicity. Animals grazing pastures in better range condition are also less likely to suffer loco poisoning.

Woolly loco can be sprayed with Grazon P+D or Tordon, but Reagor warned that the plant actually becomes more toxic and palatable after chemical treatment. For that reason he recommended keeping animals out until the plant has completely dried up.

Garboncillo is an annual loco that is restricted to the western part of the state. Locals, Hart said, call it rattle bush because when kicked it sounds like a rattlesnake. The plant has inflated lightweight pods, and the flowers, Hart said, are fairly inconspicuous, unlike woolly loco. Because it's an annual it is a prolific seed producer. It needs moisture and therefore grows in valleys that receive runoff or around tanks and in bar ditches.

Both dry and green garboncillo is toxic and livestock readily eat the dead stems remaining after dieback at frost. Horses are particularly susceptible to this plant, but it's also toxic to sheep, goats and cattle.

Lambert crazyweed is a perennial legume that often forms colonies by spreading from short rhizomes with larger plants forming mounds. It is found in North Texas and the Panhandle. This plant, though of another genus, has the typical locoweed flower with a smaller, longer, linear type seed pod. The leaves are longer and narrower than those of the other loco weeds.

Ergot poisoning occurs when favorable conditions allow parasitic fungi to infest the seedheads of certain grasses and produce ergot toxins. Fungal growth replaces much of the grass seed, which turns an uncharacteristic color and sometimes ends up as much as four times the normal size.

Two types of ergot poisoning have been described: nervous ergotism and gangrenous ergotism. Clinical signs of nervous ergotism include extreme nervous behavior and elevated body temperature, respiration rate and pulse rate. Animals exhibit a "sawhorse stance" and lean on stationary objects or each other for balance. Eventually the animals go down and are too uncoordinated to rise.

Gangrenous ergotism may include abortion or lameness and sloughing of the ear tips, hooves or tail switches.

Ryegrass can be affected with ergot, particularly in East Texas where rainfall is more abundant. The same ergot body can affect all the cereal grains, Reagor noted. Ryegrass ergot causes gangrenous ergotism.

Poisoning may be prevented by harvesting ryegrass during or before the early dough stage of seed development.

Dallisgrass ergot typically occurs in years when there is good moisture. The ergot body grows inside the seed and causes the seed to swell up.

If this seedhead is consumed, cattle develop what is known as dallisgrass staggers. It is similar to bermudagrass staggers; animals become hyper-excitable and begin jerking and shaking. The seedhead on this plant might also carry a pink colored fungus, Reagor said, that causes abortions in cows.

"We can have a lot of death loss in cattle on dallisgrass ergot in the summertime," Reagor said, adding that calves are known to selectively eat the infected seedheads.

"In most cases, if the animals are removed from the field in time and are kept in shade and get good feed and water, they will recover."

Horses that are infected and come down with the nervous ergotism sometimes have to be euthanized because they will often continue to do things that hurt themselves, such as continually running into a fence.

Before the advent of round bales, hay was usually free of any ergot-infected seedheads because they were knocked off before baling. That's not so much the case with round bales.

Tobosagrass ergot, Reagor said, is not nearly as common as some of the others, mainly because it takes moisture for these ergots to infect the plant and in West Texas where tobosagrass is common, moisture is not usually plentiful enough to cause problems.

Rayless goldenrod is another toxic plant that causes a completely different set of problems when eaten in large enough quantity. In cattle this plant produces clinical signs referred to as the trembles. Cattle that eat this plant are hyper, they shake, jerk and tremor, and this is exacerbated by exercise.

This plant grows in far West Texas, though some other species of goldenrod can be found in South Texas, Reagor told listeners. Sometimes this particular plant is confused with snakeweed, but he pointed out that snakeweed has a much finer leaf. Rayless goldenrod also is generally a much more robust plant that can grow to three feet in height. The flowers are similar on both of these plants, but goldenrod flowers tend to grow more in a bunch rather than scattered out over the plant. The plant dies back in the winter.

Rayless goldenrod is an extremely toxic plant with the same toxic principle as white snakeroot. Snakeroot problems in Texas are limited to sheep and goats, but rayless goldenrod can poison all classes of livestock. It was particularly troublesome for cattle producers in the Pecos River bottom. It is toxic year-round, even in the dormant state.

The toxic compound, tremetone, is passed through the milk. Therefore a calf whose mother has been grazing goldenrod will show clinical signs caused by the toxicity.

In horses tremetone can cause death by destroying the heart. Sheep and goats, on the other hand, suffer from liver damage.

Most poisoning from this plant occurs in late fall and early winter. A lethal dose generally consists of one to 1.5 percent of the animalís weight consumed over two to three weeks.

There is no specific treatment for poisoned animals, Reagor said.

"Remove them from the area and give them good quality hay and water. Purgatives and laxative feeds may aid in recovery. Orally administering activated charcoal at one gram per kilogram of body weight may also be helpful. Lambs and calves should be weaned and all milk from the affected females should be discarded," he told the group.

Chemical control may be used when the infestation of rayless goldenrod is particularly severe. Escort or Tordon 22K may be applied in the fall using the same basic treatment procedures as for snakeweed.

A couple of sennas found in Texas are toxic to livestock. The toxic agent is unknown. Twinleaf senna is found in western Texas through the central part of the state and is common in the Edwards Plateau region. It grows on shallow limestone hillsides.

As its name suggests, the plant has a pair of leaves that are identical to each other. It also has a showy yellow flower that is easily identified by its particular color, Hart said. It has a ribbed pod that is common in all the sennas.

Reagor has been involved with twinleaf senna since the diagnostic lab opened its doors in 1969.

"A vet out in West Central Texas wanted to find out what was killing calves down in that area every spring. We followed the death losses around Sonora and Kerrville and eventually narrowed the problem down to this particular plant."

These plants have a compound that causes muscle damage by destroying the energy-producing systems within the cells. Clinical signs for cattle consuming this plant are diarrhea, weakness, and dark urine; cattle are alert but down, and they finally die.

"This cow will probably disappoint you more than any other cow youíll ever deal with because this cow looks good. She just canít get up. You take her water, sheíll drink, sheíll eat. She just canít get up," he noted. "The problem is that this toxin not only affects the skeletal muscles, it also affects the cardiac muscle, and in two or three days that animal will be dead. That's the case in all the sennas when consumed by cattle."

The sennas are not particularly toxic to sheep, and many producers use sheep as a management tool. Goats, on the other hand, are very susceptible. In goats the toxic compound causes heart damage.

"You won't see many downer goats," Reagor remarked. "Instead you get acute death."

In studying this plant, it was discovered that ranchers who had a good mineral program in place didnít have as much of a problem with twinleaf senna compared to those who had no mineral program.

"We learned very quickly we could stop death loss of twinleaf senna in nearly every instance just by feeding a good phosphorus mineral."

Individual plant treatment usually works best when control is necessary. Weedmaster or Grazon P+D in one percent solution is the recommended treatment.

Coffee senna is more common in East and East Central Texas. It, too, has the typical senna flower. The one difference between this and twinleaf is the seedpod. The pod on coffee senna tends to be erect, and in that way it is easily distinguishable from twinleaf. Another distinguishing characteristic of this plant is that the green leaves release an unpleasant smell when pulled from the stem.

"Nothing will eat it at that stage, but as soon as the bean pod matures it loses its stink and becomes palatable," Reagor noted. "Generally after first frost is when we begin to have a lot of problems with coffee senna poisoning, typically east of College Station and down along the Coast, not quite to Corpus."

The clinical signs of this plant are the same as with twinleaf senna. Coffee senna doesn't compete with grasses at all, and for the most part is only found in localized small clusters. Simply pulling the plant is effective when it is confined to small areas. If it covers a larger area, the infested area may need to be deferred after frost.

Sicklepod senna has semi egg-shaped leaves that are wider at the tip than where they attach at the stem. The seedpod, as the name indicates, is shaped like a sickle.

"This plant stinks a little but not nearly as bad as the coffee senna," Reagor noted. "It also tends to be consumed when the leaves and pod are green. The dry mature seed is not very toxic."

This particular plant can be a problem when grown in fields cut for silage or green chop. Pastures in poor range condition where this plant is growing should not be grazed by livestock.

Several of the nightshade plants can cause serious illness in livestock.

Silver leaf nightshade is easily recognized by most landowners. It is an upright, prickly perennial in the potato family, Hart said. Most of them have spines on the stems, a long, narrow leaf shape and a tomato-type flower.

It grows throughout most of the state, but livestock generally won't consume enough to cause problems unless they're forced to eat it. Unfortunately, Reagor said, he knows of case after case where this has happened. The most recent case he remembers was a couple of summers ago when cattle were penned in a water lot and about the only thing to eat was the nightshade with its green and yellow berries. The cattle were left in the pen overnight, and the next morning were shaking, hyperexcitable, down and dead.

"The bottom line is that rancher lost seems to me like 25 to 30 cows."

The toxic agent is solanine and the leaves and fruit are poisonous at all stages, but the ripe fruits have the highest concentration of the toxic agent. It is poisonous to horses, sheep, goats, cattle and even humans, but sheep and goats are more resistant than cattle.

Nightshade poisoning causes central nervous system problems. Symptoms are incoordination, excessive salivation, labored breathing, progressive weakness or paralysis, and nasal discharge. It can also cause gastrointestinal problems like nausea, abdominal pain, vomiting and diarrhea. Affected animals should be moved as little as possible and should be fed good quality hay and water.

Grass hay with silverleaf nightshade in it is usually not a problem because the hay is usually cut prior to berry formation.

Buffalobur is an annual nightshade that has a different leaf shape than silverleaf but the same tomato-like flower. The leaves are spiny and the seed pod looks like a bur of some sort. This plant is generally found in low areas where there is a little extra water.

"You wouldnít think that anything would eat this plant, but never say never," Reagor told listeners. "There was a bunch of mature dry buffalo bur in a corner of a wheat field. Those cattle were looking for roughage and they mowed the buffalo bur down."

Western horse nettle has pods that grow in clumps and they're slightly larger than the pods on silverleaf nightshade. The leaves on this plant also are thornier than on the other nightshade plants. Horse nettle typically grows in loamy prairies all over Texas except the far west.

Cattle consuming the dry berries over 60 days in low levels wonít show the typical nightshade toxic signs, but will show signs of what is known as crazy cow syndrome. The toxic agent destroys the brain cells that control rapid movements, Reagor noted. When the animal tries to make quick movements it falls down. Affected animals do not return to normal and therefore he recommended that they be sold on the rail.

Coulterís Conyza is a herbaceous annual of the sunflower family that grows three to six feet tall. It is found in draws and bottoms all the way out to the Trans-Pecos. Horsetail conyza, a close cousin, grows further to the east but in the same kind of habitat. This plant is unpalatable, Reagor said, and not commonly consumed but it will be if it's sprayed with 2,4-D.

The toxic agent, which is unknown, causes polio in cows.

Smallhead sneezeweed is an erect, branching annual that grows around stock tanks and is most common in the western half of Texas. The plant is most toxic in its mature state. As little as a quarter of one percent of an animal's body weight produces acute poisoning and death.

Signs of illness appear within a few hours of consumption and include weakness and staggering, diarrhea, vomiting green material, grinding of teeth, bloat and salivation, to name a few. Postmortem examination reveals severe lesions in the GI tract.


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