Plants Poisonous to Live Stock

CHAPTER I. Introduction.

INTRODUCTION.

=What is a Poisonous Plant?= As will be shown later, so-called “poisonous” plants differ widely in “degree of harmfulness,” and it is highly probable that under ordinary conditions many of the plants commonly reputed to be poisonous are really almost or quite harmless. It is possible, however, that a plant usually unsuspected may on occasion prove noxious—for example, Nepeta Glechoma (p. 96), included as suspected of poisoning horses. For these reasons, no line of demarcation can be drawn to separate actually poisonous plants from those which are suspected or are almost certainly quite harmless; and a large number of species is included in Chapter VII as suspected, many of them, however, being almost certainly more or less poisonous in certain circumstances. In many cases it is practically impossible to come to any conclusion as to the degree of toxicity of a plant, owing to the want of exact information. Many plants are quite harmless except when affected by fungi, moulds, etc.

A really poisonous plant may be defined as one a small quantity of which when eaten induces some form of indisposition with irritant, narcotic, or nervous symptoms, with serious or even fatal consequences either immediately or by reason of cumulative action of the toxic property.

=Harm done by Poisonous Plants.= A perusal of the following pages will afford convincing proof that the question of the general “wholesomeness” of wild plants is worthy of serious consideration by all who are interested in the practice of agriculture. Still more important is a satisfactory knowledge of the extent to which plants are actually poisonous—that is, sufficiently injurious when eaten in small or large quantities to induce more or less severe indisposition, illness or death, with the consequent losses which such bring in their train—loss of milk and meat production in the case of cattle, of meat and wool production in sheep, of power in the horse, of expenditure in attendance and veterinary treatment generally, and possibly total loss by death of the animals concerned.

The losses due to Poisonous Plants in Great Britain happily afford no comparison whatever with the immense losses sustained in some other countries, such as the cases of lupine poisoning mentioned at p. 29, but deaths are sufficiently numerous to make it certain that financial losses are in the aggregate very heavy. In this connection it may suffice to refer to the many cases of yew poisoning, the losses due to Umbellifers (pp. 36–42), and the instance reported in the Staffordshire Weekly Sentinel in relation to meadow saffron and water hemlock (p. 80). Further, it appears to be extremely likely that many losses due to unascertained causes are really due to plant poisoning. For this reason veterinary surgeons will be well advised always to consider this possibility and, if need be, to obtain the services of a trained botanist to survey the farm or field involved, with the object of deciding whether poisonous plants are present.

=Circumstances in which Poisoning occurs.= It may be assumed that many plants are to a considerable extent protected from animals by the fact that they have an unpleasant odour, are acrid or bitter to the taste, or are actually toxic in character, just as others assume such protective devices as spines. In a state of nature animals appear to avoid instinctively such plants as are toxic or “unwholesome,” and to be less readily poisoned than are domesticated animals living under artificial conditions. Indeed, it has been remarked that farm stock reared in a locality where certain poisonous plants abound are much less likely to be injured by these plants than animals imported from a district where they do not occur.

The individuality of stock is also a factor which may be responsible for poisoning, some animals having what may be described as a depraved appetite for unusual and unappetising food plants. It would appear that animals are often tempted to eat dark-green plants of luxuriant growth which are soft and succulent. This is especially true when the plants are young and tender, particularly as regards sheep, which, however, usually avoid tall, old rank-growing and coarse herbage—unless absolutely pressed by hunger. Cattle, however, are not so particular, and will commonly eat large coarse-growing plants.

Sheep have been observed to be particularly variable in their choice of food plants, not only individually in the flock, but from day to day. Chesnut and Wilcox remark that “there seems to be no way of accounting for the appetite or taste of stock. This statement is perhaps especially true of sheep. We have often observed sheep eating greedily on one day plants which they could scarcely be persuaded to eat on the following day on the same range.” In the case of one flock of sheep on a foothill range at an altitude of 4,600 ft. “a few of the sheep were observed eating large quantities of wild sunflower (Balsamorhiza sagittata), a few ate freely of false lupine (Thermopsis rhombifolia), some confined their attention largely to the wild geranium, while others ate false esparcet (Astragalus bisulcatus) almost exclusively. Two sheep were seen eating the leaves of lupine, and about fifty ate a greater or less quantity of Zygadenus venenosus, while the majority of sheep in the band fed exclusively upon the native grasses on the range.”

Footnote 1:

“The Stock-Poisoning Plants of Montana,” V. K. Chesnut and E. V. Wilcox. Bul. No. 26. U.S. Dept. Agric., Div. Bot., 1901.

Horses also have been known to acquire in America a depraved appetite for horsetail and loco-weed.

The different species of live stock are often quite differently affected by poisonous plants, some being very susceptible to a given plant while others may be little or not at all susceptible. One species (e.g. the pig) may readily vomit the poison of a plant which is emetic, while another (e.g. the horse) may be unable to do so and hence be the more seriously injured. The variability of the different classes of live stock in this respect is frequently brought out in Chapters II to VI. Poisonous effects may also vary with the individuality and age of animals of the same species.

At certain periods of the year—e.g. in early spring, and during dry summers,—there may be a scarcity of green herbage, and this may induce animals to eat any green plants which are especially early, including poisonous ones, which they would otherwise refuse.

In some cases poisonous plants which do not lose their toxic properties on drying (e.g. meadow saffron) may be included in hay, and hence find their way to stock in such a form that they may not be distinguished. It has been found, however, that some poisonous plants or parts of them are refused by stock when mixed with good herbage in hay. Care should be exercised that poisonous plants are not included with hay or green fodder, and in cases of poisoning all forage should be examined.

Animals may also be poisoned by certain toxic seeds (e.g. corn cockle) fed to them with cereal grains, in feeding stuffs generally, or in the refuse seeds from the sources mentioned. Here again judgment is necessary, and it is probably advisable on all counts to burn the weed seeds and similar refuse from the sources mentioned. Poisonous seeds may occur in low quality feeding stuffs, and poisonous seeds of foreign origin are occasionally sold for food purposes owing to the mistaken idea that they are a valuable addition to the ration (e.g. the poisonous “Java” beans). In any case in which an animal is believed to have been poisoned purchased feeding stuffs should always be considered as a possible source of injury and be submitted to examination.

Clippings and trimmings from gardens and shrubberies have proved a more or less common cause of live stock poisoning, such material being too often carelessly thrown out for animals to pick over. In such circumstances it may quite easily happen that the animals get yew, daphne, privet, rhododendron, azalea, solanums, and other plants of a poisonous character. For this reason it is better to destroy such trimmings, etc., by burning them, or by adding them to the compost heap as the case may be.

A further source of poisoning must be noted here—fleshy and parasitic fungi (toadstools, rust fungi), moulds and similar organisms. Many toadstools are directly poisonous when eaten, but the microscopic organisms are probably in themselves harmless, though taken with food which they are responsible for injuring (bad hay, cakes, etc.), the poisoning being due to the changed and damaged feeding stuffs, or possibly to poisonous principles directly elaborated by the microscopic fungi. Fungi and related organisms cannot be dealt with in this volume, but it may at least be said that the use of mouldy hay and similarly affected feeding stuffs is attended with some danger, which is not yet very clearly defined.

=Effect of Soil, Climate and Cultivation on the Toxic Properties of Plants.= In general, wild poisonous plants are richer in either alkaloids or glucosides than the same species when cultivated, though there are exceptions. In many cases it is found that plants vary considerably in toxicity, or the percentage content of the poisonous principle, according to soil, light, moisture, etc. Solanaceous plants in particular vary in this way, and one or two instances may be given as examples. Solanum nigrum varies so much that it has been regarded as harmless in one country and quite poisonous in another (p. 52).

Continue reading Plants Poisonous to Live Stock free in the Wunder reader →