Poisonous Plants

FOREWORD:

POISONOUS plants are probably responsible for greater losses of live stock than is commonly believed. The number of wild plants that are seriously poisonous is perhaps small compared with the total species included in the British flora, but there are many species that are very common and that may occasionally cause serious losses of farm stock, while they may also cause illness and death to human beings, particularly children. When poisonous plants occur in quantity, they may be unavoidably harvested with hay or other crops and thus later be given to stock; or they may be eaten in the green state in the open fields and along hedgerows. Many cultivated plants and trees are also poisonous and are often responsible for trouble with live stock, on which they have an irritant or poisonous effect. The incidence of poisonous plants on the farm was regarded as sufficiently important for the Ministry to deal with the subject in one of its Bulletins, and Mr. H. C. Long was confidently anticipated that the book would be widely welcomed by farmers-for the reason that it is simply written, is well illustrated and fills a definite need. The result has confirmed this belief, for over a period of ten years sales have averaged 330 copies annually. A 2nd edition was overdue, and this has accordingly been prepared by the author. Considerable care has been taken to give references wherever this seemed desirable, but the author is greatly indebted to many authorities almost too numerous to mention individually. For any oversight in this direction he hopes he may be pardoned.

When it is realized that the presence of meadow saffron or water hemlock in a meadow may occasion the loss of valuable animals, or that the ingestion of certain wild berries by a child may result in death, it will be clearly seen that some knowledge as to which plants are poisonous is desirable, not a only on the part of farmers and others, but all dwellers in the countryside. After reading the following notes, a farmer may possibly realize that mysterious losses among his stock have probably been due to one or other of the poisonous plants described in this volume. A simple example will suffice. In 1909 it was stated by Mr. J. C. Rushton, then Agricultural Organizer for the Staffordshire Country Council, that a farmer in south Staffordshire in one year lost 17 milking cows; in the autumn of 1908 he lost seven calves, and in 1909 he lost a number of sheep and a cows. Investigation showed that a field associated with the losses contained a large amount of meadow saffron and water hemlock, and that these plants were the cause of the loss of stock (Staffs Weekly Sentinel, August 21, 1909). Laburnum, yew, and other noxious plants may be browsed upon by stock in fields near large gardens; others, such as box, rhododendron, monkshood, hellebore, and larkspur, may be present in clipping and other rubbish form gardens and shrubberies. Poisoning of stock by horsetail and bracken is much less readily recognized, but as these species are almost ubiquitous their presence may well make them suspects when diagnosis presents difficulty.

Apart from indigenous plants of the farm well known to be poisonous, there are quite a number that are suspected of being poisonous or harmful. In addition, may plants, though perhaps not really poisonous, do much damage by tainting the milk of dairy cows and the products made from it, as well as the flesh of animals. It would not be possible in this little volume to exhaust the whole subject, but some account is given of plants that might well be the cause of loss, together with notes on miner and suspected species, plants that taint the milk of cows, and plants that cause mechanical injury to stock. The symptoms poisoning by the various plants can-not generally be given here. For information thereon, as well as in regard to the antidotes or remedial measures, reference may be made to the works mentioned on p. 102. Further, it there is suspicion of poisoning of stock, a veterinary surgeon should at once be called in.

Among the wild plants on a farm there may be several species capable of proving seriously harmful and even deadly to live stock. Certain of them are weed pasts in the ordinary sense to the term, but the harm they may do is immensely in-creased by reason of their poisonous properties. Some are implicated only to a slight extent, whereas others-fortunately fewer in number-speedily cause symptoms of poisoning often ending in death if only a small quantity be ingested. Others may only cause poisoning if they are consumed regularly over several days or weeks, the poison being cumulative in the system.

A number of points must be borne in mind when poisonous plants are under consideration. If an animal is found to be suddenly ill from some unknown cause, the veterinary surgeon called in may suspect some form of poisoning. It is then desirable that, after treatment of the sick animal, an immediate search of the pasturage should be made, or it may be of the dried fodder and other feeding stuffs being used, the object being to determine the cause and prevent further loss. It may be necessary to being in a trained botanist to identify any plant that may be poisonous. This is not all, as for poisoning to be caused, it is necessary that the plant concerned shall be presents in sufficient quantity to enable an animal to take enough to bring about immediate symptoms of poisoning; or, alter-natively, that, with some species, small quantities shall be eaten for a continuous period, the poison being cumulative until a stage is reached when the breakdown occurs and poisonous effects are manifested.

Animals seem to differ widely in the readiness with which they consume harmful wild plants, some instinctively avoiding them. This is, of course, especially so when keep is plentiful or the harmful species is acrid or unpleasant to the taste or smell. It is, however, a surprising fact that some animals are apt to eat many things that are usually avoided. Chesnut and Wilcox, in the United States, found 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 America, also, horses have been known to acquire a depraved appetite for horsetail.

Not only may heavy loss be caused by death or illness of stock, but poisonous symptoms are often accompanied by reduction of milk yield, or the milk is affected in a deleterious manner as regards taste or colour, or, exceptionally, conveyance of the toxic principle.

Mattes are complicated by the fact that the same species is not necessarily equally poisonous in all districts, possibly owing to differences in soil and climatic conditions, nor at all seasons, probably because of difference in age. The point that there is great variation in the toxicity of poisonous plants has been discussed by F. N. Howes (Kew Bul. Misc. Inf., 1993, p. 305). Another point is that all parts of a poisonous plant have not the same effect, some parts being more toxic than others; or some parts may be harmless and other poisonous. Again, whereas members of the buttercup family loss their poisonous properties when dried in the buttercup family lose their poisonous properties when dried in the form of hay, others, e.g., meadow saffron, are strongly poisonous both bride and in the green state.

Though the species of poisonous plants are not confined to grass land, the more readily determined cases of poisoning are likely to be those involving stock at pasture, if only because stoke seldom have the opportunity of taking plants on arable land, except in so far as far as sheep are concerned. In ordinary pastures and meadows, along the dykes of water meadows, by hedgerows, under shady trees and alongside of woods, poisonous plants may often escape notice until injury has been caused. Cuttings of some plants such as yew, laburnum, box, monks-hood, hellebore, larkspur, may be thrown out with lawn mowing and trimmings form gardens, and in this way poisoning may occur. If keep is short, as during a drought, and animals are to some extent driven by hunger, they are more apt to eat whatever is luxuriant, green and succulent.

A point deserving of notice is that the different classes of live stock vary considerably in their susceptibility to poisonous plants, while the individuality and age of the animals may induce greater or loss effect. This point has also been made by Howes (loc.cit.). Generally, the effects of plants on animals are widely divergent and the common meaning of the designation “poisonous” seems to vary as much as the persons who use it; but the author has elsewhere defined a really poisonous plants 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.”

When it has been determined that a poisonous plant is presents, there can be little question of the action that should be taken. Stock should be moved to fresh pasture until it has been possible to make the infested one safe for them by through removal and destruction of the harmful plants. In some instances this may only involve cutting over and burning of the rootstock may be very desirable or essential, as when certain perennial water-side or hedge weeds are involved. To be through, treatment must be followed up by repeated observation and regular removed of any fresh plants that appear.

It may also be observed that some poisonous principles are widely distributed in plant species. This may be indicated by the fact that in 1992 Jonck published a list (incomplete) of over 100 species of plants known to contain cyanogenetic compounds (yielding prussic acid in over 20 natural orders. (T. A. Henry : On the Occurrence of Prussic Acid and its Derivatives in Plants, Science Progress, July, 1906.) Since that date the number of plants founds to contain such compounds has increased.

There is also a legal aspect where poisonous plants are concerned, and this is deserving of consideration. For example, it has been held that where a yew tree grew through and over a fence and projected on to a meadow occupied by the plaintiff, the owner of the tree was liable for the loss of a horse that was poisoned by eating the foliage of the tree.

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