WARD T. HUFFMAN, EDWARD A. MORAN, AND WAYNE BINNS.
PLANTS that poison livestock can grow anyplace, but they are a serious problem mainly in the western grazing areas where overgrazing has impaired or destroyed the good but less sturdy forage plants.
The poisonous plants usually grow among forage plants and so are available to grazing animals. Only a few are agreeable to the taste, however, and animals avoid the toxic plants unless there is a shortage of feed and better vegetation.
Overgrazing is a major factor in livestock losses from poisonous plants. Overgrazing has increased in some sections because moisture deficiencies have reduced the growth of forage. Hungry animals feed on whatever is available.
Sometimes harmful plants are harvested with the hay and their seeds become mixed with grain. Then animals can hardly separate the good feed from the bad. Livestock owners have considerable control over conditions conducive to poisoning by plants.
Some plants contain acute poisons and produce visible symptoms or death soon after they are eaten. Others may be eaten for some time before any noticeable effects are apparent. Most poisonous plants may be eaten for a considerable time with little or no ill effects.
IT IS NOT EASY to control poisonous plants in pastures and on the range. Plowing and cultivation usually eradicate them, but in some areas, such as the western grazing lands, these methods are not feasible because of expense, the time they take, and the amount of benefit. Sometimes the plants are pulled up, grubbed out, or killed with herbicides, but that is slow and expensive even under favorable conditions.
Many poisonous plants are distributed so widely over grazing areas of limited value in the Western States that the cost of eradication would be much greater than the benefits. A more practical procedure is to remove the toxic plants from limited areas, including trails and watering places. The method of eradication used would depend on the character and growth habits of the species, the other plants with which the toxic plants grow, and the type of soil.
When eradication is impractical, a system of range and pasture management can be worked out to permit the use of the forage crops without excessive livestock losses. That is largely a matter of wise control of grazing.
Poisonous plants often are the first to start growth in the spring and may harm livestock if too early grazing is practiced. If pastures and ranges are stocked to full capacity in normal years and the number of livestock is not reduced in drought years, the usual forage can be supplemented with other roughage or feed in order to avoid injury to the existing vegetation and losses of animals from the poisonous plants.
Another aspect of control is that one species of animals may avoid certain plants, or one species may not be injured by plants that poison another species. Losses then may be avoided by permitting only the animals least affected to graze them.
Some examples: Horses seldom eat cyanogenetic plants plants that can produce hydrocyanic acid in toxic amounts, but cattle and sheep frequently do eat such plants and are poisoned by them. Pastures that contain cyanogenetic plants should be used by horses in preference to cattle and sheep. Horses are more frequently poisoned by ragworts or groundsels, which are species of Senecio, than are cattle or sheep, and sheep are less susceptible to their poisoning than are cattle. Pastures containing ragworts should be used by sheep in preference to cattle or horses. Cattle often are poisoned on larkspur. Sheep, however, can consume large amounts of larkspur without being poisoned but with apparent benefit. Only under abnormal conditions are sheep ever poisoned by larkspur on the range. Horses never eat enough of the larkspur to produce any ill effects. Pastures containing larkspur should be used by sheep and horses but not by cattle.
Another aspect: Some plants, such as the sorghums, become toxic under certain conditions. Sorghum in the mature stage does not contain any appreciable amount of potential hydrocyanic acid, but the young plants, or suckers (young branches from the roots), of mature sorghum may contain very much potential hydrocyanic acid. Arrowgrass grown on water-covered or very wet soil is far less poisonous than arrow-grass that continues to grow on soil that has dried after the water has receded. Oil meal made from immature flaxseed is more apt to be poisonous than oil meal made from thoroughly ripe flaxseed.
TREATMENT OF ANIMALS poisoned by plants usually is unsatisfactory and useless, because most of the damage may have been done by the time the poisoning is discovered.
Certain feeds or medicines that have some preventive value are described later in connection with plants that contain selenium. Good care and a Symptomatic treatment (treatment that will reduce symptoms) will save some poisoned animals. The outcome in each case depends largely on the amount of toxic material that has been eaten and assimilated. Treatment usually is directed toward eliminating any of the toxic substance that still remains in the digestive tract. In chronic poisoning, recovery may follow a change of feed, especially if green feed is available; good care, with plenty of water and the right kind of feed, will do much to hasten recovery. (Later we suggest treatments for three types of poisoning.)
It is well to know something of the chemistry of the poisonous elements, especially those in the compounds that are physiologically active. Knowing whether the substance is an alkaloid, a glucoside, or something else makes it possible to determine by laboratory examination whether a sample of the plant is potentially deadly and to detect the poison in the tissues of animals so that a diagnosis can be made in obscure or doubtful cases.
ALKALOIDS are substances that are like the alkalies. An alkaloid turns red litmus paper blue, reacts with an acid to form a salt, and has some other properties that solutions of the alkali metals have, such as soda or potash.
The alkaloids are organic substances that contain nitrogen. Some of the alkaloids are quite stable and may be detected by a chemist in the plant tissues or the tissues of poisoned animals.
It is important for the farmer or student to know that certain groups or families of plants, such as the legume, lily, buttercup, potato, and some other families, are more likely to contain alkaloids than some other groups.
Some of the groups do not so metabolize their nitrogen as to yield alkaloids. The large and important mint family seldom contains any alkaloidal plants. The aster, or composite, family is another nonalkaloidal group, although there is an outstanding exception in the ragworts, or groundsels, of that family. The grasses are not characteristically alkaloid bearing, although darnel yields loliine, which is a true base.
A well-known alkaloid is strychnine, which is obtained from poisonnut (Strychnos species), a member of the logania family, whose members are mostly tropical plants. Morphine is an alkaloid that can be separated from the drug opium (an extract from certain kinds of poppy). Other well-known alkaloids are atropine, nicotine, and solanine, from the potato family; aconitine and several alkaloids of the larkspur group, from the buttercup family; zygadinine and colchicine, from the lily family; and physostigmine, lupinine, and other lupine alkaloids, from the legume, or pea, family. Names of alkaloids usually end in "-ins."
Alkaloids occur in many stock-poisoning plants. Among them are the larkspurs, lupines, deathcamas, groundsels, Dutchmans-breeches and other plants of the Dutchmans-breeches family, poison-hemlock, wildtobaccos, crotolarias, and African-rue.
Larkspurs seem to attract cattle because of the pleasant acidity of their leaves, which is refreshing in hot weather. They are one of the few poisonous plants that are palatable. The larkspur alkaloids are complex.
Delphinium barbeyi, one of the tall larkspurs, and D. menziesi, a low species, are the main poisonous species, although most of the species of Delphinium are dangerous, especially when the plants are small or when they are available in quantities. D. occidentale, a tall and comparatively nontoxic larkspur, resembles D. barbeyi and often is mistaken for it. D. occidentale contains about 1 percent of an alkaloid.
A treatment recommended for cattle poisoned by larkspur during drives and roundups is a subcutaneous injection of a mixture of 1 grain of physostigmine salicylate (also called eserine), 2 grains of pilocarpine hydrochloride, and one-half grain of strychnine sulfate, thoroughly dissolved in sterile water. This formula applies to an animal weighing 500 to 600 pounds. For a larger steer or cow of 1,000 pounds or more, the dose should be twice that amount. The medicine relieves constipation and stimulates respiration. The materials can be obtained from a druggist.
LUPINES, also known as bluebonnets and by other local names, belong to the legume family. Some species are harmless, at least at some stages of growth, and are excellent feed for grazing animals. Others are dangerous at certain times. Some are toxic at any stage of growth.
The alkaloids in lupines have the peculiarity that slight alterations in the molecular structure may convert the toxic alkaloid into a comparatively nonpoisonous substance, and vice versa. The alterations may take place in the plants and may account for the variations in the toxicity of the growing plants.
Reports from Germany in the 1860's attributed great losses to the yellow lupine (Lupinus luteus) and other lupines. Actually, however, the losses were due to molds. In this country losses from lupines have been due to alkaloidal poisoning.
Deathcamas (species of Zigadenus) are another group of alkaloid-containing plants. They are grasslike and not conspicuous until they bloom. They are also known as the poison sego, mystery-grass, lobelia, soap plant, alkaligrass, waterlily, squirrel food, wild onion, and hog's potato.
Species of Senecios, or groundsels, have caused a number of losses in livestock in Texas and other States.