CAMBRIDGE AGRICULTURAL MONOGRAPHS
PLANTS POISONOUS TO
LIVE STOCK
CAMBRIDGE UNIVERSITY PRESS
C. F. CLAY, MANAGER
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[Illustration: _a_ Reddish-brown to reddish-purple “Java” Beans
(_Phaseolus lunatus_); _b_ “Red Rangoon” Beans (_P. lunatus_); _c_
“Large White” Beans (_P. lunatus_); _d_ Castor Oil Beans (_Ricinus
communis_); _e_ “Indian Peas” (_Lathyrus sativus_), from Bombay; _f_
Ergot (_Claviceps purpurea_), from Spain. All natural size.]
PLANTS POISONOUS TO LIVE STOCK
BY
HAROLD C. LONG, B.Sc. (Edin.)
of the Board of Agriculture and Fisheries
Author of _Common Weeds of the Farm and Garden_
Cambridge:
at the University Press
1917
PREFACE
As in the case of a previous volume, _Common Weeds of the Farm and
Garden_, the preparation of this handbook was undertaken because of the
great lack of readily available and reliable information on the subject
in English scientific literature. Many of the facts were known to a few
interested persons, but many others were so scattered here and there in
technical reports and journals that they were scarcely known even to
expert chemists and botanists. The bringing of this information together
in some sort of order has involved considerable labour extending over
several years, but if the volume be found helpful to those for whose use
it has been prepared I shall feel more than gratified.
That the subject is of importance is fully realised by farmers and
veterinary surgeons alike, for the annual loss of stock due to poisonous
plants, though not ascertainable, is undoubtedly considerable. It was
felt that notes on mechanical injury caused by plants and on the
influence of plants on milk might usefully be included, as in some
degree related to poisoning; this has therefore been done. On the other
hand, a number of cultivated plants (_e.g._ _Rhus_, _Wistaria_) which
are poisonous have not been included because exotic and hardly likely to
be eaten by stock. Fungi generally also find no place in the volume, as
they are sufficiently extensive to deserve a volume to themselves, and
are far less readily identified than flowering plants.
The dividing line between plants which are actually poisonous and those
which are only suspected is far from clear, but a division was
considered desirable for the convenience of the reader, and an endeavour
has been made to give a sound but brief statement as to the present
information on plants poisonous to live stock in the United Kingdom,
with symptoms, toxic principles, and a list of the more important
references to the bibliography in relation to each plant included in
Chapters II to VI (the numbers corresponding with the numbers in the
Bibliography).
Regarding symptoms it is to be regretted that in many cases they appear
to be the result of injections of the toxic extracts, and not
observations made after natural poisoning by ingestion of the plants.
Further, there may frequently be doubt as to the identification of the
plant suspected of causing poisoning; indeed, in some cases it is
possible that the identification rests on the veterinary surgeon or the
stockman _thinking_ a certain plant is the cause. The most complete and
systematic account of European poisonous plants is that of Cornevin
(1887), and references to poisonous plants in the ordinary literature
are heavily indebted to him. In so far as the toxic principles of the
plants are concerned, however, his book is in many instances no longer
reliable.
The chemical formulae, quoted for the use of students and research
workers, have been checked by consulting works by the following authors,
the reference to the bibliography being given in brackets: Henry (128),
Dunstan (76), Allen (4), Haas and Hill (114), Thorpe (240), Van Rijn
(252), Kobert (161), Esser (81), and Beilstein (16).
Apart from the literature consulted I desire to acknowledge my great
indebtedness to the Board of Agriculture and Fisheries for kind
permission to make use of official records; to Mr F. W. Garnett,
M.R.C.V.S., for kindly reading the proofs from the veterinary
standpoint; to very many Experiment Stations, State Departments of
Agriculture, and other authorities in Australasia, America and the
Continent of Europe, for assistance given and literature sent; to Sir
David Prain and members of the staff at Kew for much friendly advice,
and aid in consulting the Kew library; to Sir James Dobbie for
permission to spend some time at the Government Laboratories to consult
certain volumes; to Mr T. H. Middleton, C.B., Dr. E. J. Russell,
Professor W. Somerville, Sir Stewart Stockman, Professor T. B. Wood, and
others, for information and many helpful suggestions; to my friend Mr W.
A. Whatmough, B.Sc. (Lond.), for many suggestions and kindly reading the
proofs; and to my colleague Mr W. R. Black for invaluable help in
preparing notes, checking data and reading proofs. To all these, and
many others who are not mentioned by name, I tender my sincere thanks.
For any shortcomings I crave the indulgence of my readers, only
requesting that they be friendly enough to spare a moment to call my
attention thereto.
H. C. LONG.
SURBITON,
_October_, 1916.
CONTENTS
CHAP. PAGE
I. INTRODUCTION 1
What is a Poisonous Plant? Harm done by Poisonous
Plants. Circumstances in which Poisoning occurs.
Effect of Soil, Climate and Cultivation on the
Toxic Properties of Plants. Variation in the
Poisonous Parts of Plants. Eradication of
Poisonous Plants. Treatment of Poisoned Animals.
Tests with Suspected Plants. Legal Aspect of Plant
Poisoning. The Toxic Principles of Plants.
II. RANUNCULACEÆ. PAPAVERACEÆ. CRUCIFERÆ.
CARYOPHYLLACEÆ. HYPERICINEÆ. GERANIACEÆ 9
III. CELASTRACEÆ. RHAMNACEÆ. PAPILIONACEÆ. ROSACEÆ.
CUCURBITACEÆ. UMBELLIFERÆ 24
IV. ARALIACEÆ. CAPRIFOLIACEÆ. COMPOSITÆ. ERICACEÆ.
PRIMULACEÆ. OLEACEÆ. CONVOLVULACEÆ. SOLANACEÆ 43
V. SCROPHULARINEÆ. POLYGONACEÆ. THYMELACEÆ.
EUPHORBIACEÆ. AMENTACEÆ. CONIFERÆ. AROIDEÆ 61
VI. DIOSCORIDEÆ. LILIACEÆ. GRAMINEÆ. EQUISETACEÆ.
FILICES. FUNGI 78
VII. PLANTS SUSPECTED OF BEING POISONOUS 92
VIII. THE EFFECTS OF PLANTS ON MILK. PLANTS WHICH CAUSE
MECHANICAL INJURY 99
IX. CLASSIFICATION OF POISONS 103
BIBLIOGRAPHY 106
INDEX 114
Photograph of three varieties of _Phaseolus_
beans, of Castor Oil Beans, Indian Peas, and
Ergot _Frontispiece_
CHAPTER I
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[1] 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).
Experiments conducted at the Arlington Experimental Farm, Virginia,
showed that in 24 first-year plants of _Atropa Belladonna_ grown in 1910
the alkaloid contents of the leaves varied from 0·334 to 0·700 per
cent., and averaged 0·547 per cent. In 1911 the alkaloid contents
(usually the average of five pickings) of the leaves of 59 plants varied
from 0·306 to 0·766 per cent., and averaged 0·532 per cent. In 1912 the
alkaloid contents (commonly the average of 5 pickings) of the leaves of
57 plants varied from 0·352 to 0·768 per cent., and averaged 0·545 per
cent. In individual plants at a single picking the highest alkaloid
content in 1911 was 0·925 and the lowest 0·200, and in 1912 the highest
was 0·882 and the lowest 0·292. (_Jour. Agric. Res._, I. 2, Nov., 1913.)
The variation in the percentage of poisonous principle was well shown in
several papers read at the International Congress of Applied Chemistry
held at Washington and New York in 1912 (see _Chemist and Druggist_
reports). For example, Carr stated that at the Wellcome Materia Medica
Farm, Dartford, Kent, the effect of manuring on medicinal plants has
been tested for some years, and the effect of the more common
fertilisers on _Atropa Belladonna_ was shown by the following table:—
────────────────────────────────────┬──────────────────────────────────
│Percentage of Alkaloid in Dry Stem
│ and Leaf
──────────────┬───────────┬─────────┼──────┬──────┬──────┬──────┬──────
│ │ │ 1906 │ 1907 │ 1910 │ 1911 │ 1912
Fertiliser │ Time of │Per acre │ 3rd │ 4th │ 1st │ 2nd │ 3rd
│Application│ │year’s│year’s│year’s│year’s│year’s
│ │ │plants│plants│plants│plants│plants
──────────────┼───────────┼─────────┼──────┼──────┼──────┼──────┼──────
Main crop │ │ │ 0·54 │ 0·34 │ 0·61 │ 0·59 │ 0·68
Farmyard │ March │50 loads │ 0·54 │ 0·34 │ 0·61 │ 0·53 │ 0·71
manure │ │ │ │ │ │ │
Nitrate │ March & │ 2 cwt. │ 0·52 │ 0·23 │ 0·54 │ 0·46 │ 0·64
│ April │ │ │ │ │ │
Calcium │ Do. │ 1 cwt. │ │ │ 0·69 │ 0·49 │ 0·75
cyanamide │ │ │ │ │ │ │
Basic slag │ Do. │ 2 cwt. │ 0·61 │ │ 0·65 │ 0·56 │ 0·84
Superphosphate│ Do. │ 5 cwt. │ 0·46 │ │ 0·81 │ 0·49 │ 0·76
Potash │ Do. │ 5 cwt. │ 0·61 │ 0·40 │ 0·75 │ 0·53 │ 0·69
──────────────┴───────────┴─────────┴──────┴──────┴──────┴──────┴──────
In considering these results it must be remembered that the soil is
naturally suited to the plant, and the percentage of alkaloid obtained
without added fertilisers is already high. The low figures obtained in
1907 were probably due to the seasonal conditions. Atmospheric
conditions have a modifying influence.
It was also shown that the Belladonna root of commerce varies greatly in
alkaloid strength. “In a number of analyses made of commercial roots,
variations from 0·27 to 0·69 per cent. have occurred. The average of
twenty-one analyses of German and Austrian commercial roots was 0·40 per
cent. Other observers have recorded similar results. Chevalier (_Compt.
Rend._, 1910, 150, 344) gives the following figures for Continental
roots: French, 0·300 to 0·450 per cent.; Austrian, 0·251 to 0·372 per
cent.; Italian, 0·107 to 0·187 per cent. Henderson has shown the average
of thirty samples of foreign root to be 0·3 per cent. It is interesting
to observe that the average of nine samples of root grown at Darenth is
0·54 per cent. In order to determine whether this variation was due to
collecting at different times of the year, roots from the same plot,
derived from second year’s plants, which were sown at the same time,
were dug up at intervals and dried. The following is a record of the
analysis of these samples:—
March, 1911 0·56 per cent.
May, 1911 0·59 „ „
June, 1911 0·53 „ „
August, 1911 0·50 „ „
December, 1911 0·59 „ „
“The amount of variation throughout the year is thus seen to be very
small.”
Dunstan (_Bul. Imp. Inst., 1905_) has shown that _Hyoscyamus muticus_
grown in India yielded 0·3 to 0·4 per cent. of hyoscyamine, but that the
same species grown in Egypt produced 0·6 to 1·2 per cent.
According to Esser no coniine is found in _Conium maculatum_ growing in
the far north. The same authority says that the root of _Hyoscyamus
niger_ is quite free from toxic properties in winter.
=Variation in the Poisonous Parts of Plants.= As will be shown in
succeeding chapters, many plants (_e.g._ meadow saffron) are poisonous
in all their parts, though the amount of the toxic substance may differ
according as to whether the seeds, leaves, stem or roots are severally
considered. In other cases one part of the plant alone is toxic (_e.g._
the seeds, as in corn cockle). Further, some species vary in the
percentage of the toxic substance in the leaves before and after
flowering. Frequently the root is the most toxic portion of the plant.
This point may be usefully recollected in relation to poisoning of live
stock, which are in general affected by the foliage or ripe seeds.
=Eradication of Poisonous Plants.= Wherever poisonous plants are found,
particularly in quantity, where they are liable to be eaten by live
stock, an attempt should be made to eradicate them. They may be simply
dealt with as weeds as may be necessary according to the species
concerned. When any difficulty is experienced in regard either to
determination of the species or to methods of eradication the advice of
the Board of Agriculture and Fisheries (Whitehall Place, London, S.W.)
should be requested. Stock should at once be removed from a suspected
pasture, which should be immediately and thoroughly examined by a
competent botanist. Harmful plants should be eradicated and their place
filled by better herbage.
=Treatment of Poisoned Animals.= This volume makes no pretensions to
deal with the veterinary treatment of cases of plant poisoning. Whenever
poisoning is suspected the services of a veterinary surgeon should be
sought without delay; the text books at his disposal will aid him in the
treatment of any case which presents unusual difficulties. The symptoms
indicated in the following pages, together with the possible discovery
of a suspected plant, may be utilised in diagnosis.
=Tests with Suspected Plants.= The action of plants on animals may be
ascertained (1) by observing the effects in cases in which it has been
established that the plants have been eaten, or (2) by direct
experimental feeding of animals with the plant. In the first case the
results may be accurate and satisfactory if observations have been made
from the outset.
As regards (2) the results may or may not be satisfactory according as
the plan pursued is sound or otherwise. For example, it cannot be
considered altogether reasonable and satisfactory to extract the
principles present in the plant, inject them into the blood stream, and
conclude from any ill effects that the animal may exhibit that the plant
is poisonous, since the substance extracted may be poisonous under such
conditions but little or not at all harmful when the plant is eaten in
the small quantities commonly taken by animals. Again, it cannot be held
satisfactory to feed an animal on a heavy and exclusive diet of the
suspected plant for a considerable period. The real test would, in
general, consist in a feeding trial in which the suspected plant
occupied a place in the ration in reasonable quantity—such a quantity as
might well be taken in natural circumstances, in view of its relative
abundance in regard to other food available; and if considered likely
that the plant would be eaten daily it may be fed regularly for some
days. Should such a test prove negative it may generally be held that
the plant is not poisonous, or only so in exceptional circumstances.
=Legal Aspect of Plant Poisoning.= There is clearly some legal liability
in regard to poisonous plants which may, by hanging over a boundary,
cause injury to a neighbour’s stock. The only cases known to the author
are in relation to the yew. In the case of _Crowhurst v. Amersham Burial
Board_ (48 L. J., Ex. 109; 4 Ex. D., 5) a Burial Board was held liable
for the loss of a horse poisoned by eating leaves of a yew tree planted
in the cemetery owned by the Board, the tree having grown through and
over their fence and projected on to the meadow occupied by the
plaintiff. In _Ponting_ v. _Noakes_ (63 L. J. B. 549; (1894) 2 Q.B.,
281) the defendant was not held liable for the death of a horse which
ate off the branches of a yew tree, because the tree did not extend up
to or over the plaintiff’s boundary, though it overhung a ditch, the
edge of which was the boundary, and was hence accessible to the
plaintiff’s stock.
=The Toxic Principles of Plants.= The poisonous substances in plants may
be grouped either (1) according to their physiological effects on
certain organs; (2) according to the principal outward and perceptible
symptoms caused; or (3) in accordance with their chemical relationships.
In regard to (1) the poisons may be nerve, heart, blood-poisons, etc.
(2) The poisons may be acrid, narcotic, or both. _Acrid poisons_ are
those which cause irritation or inflammation of the digestive tract
(_Euphorbia_, _Ranunculus_, _Daphne_, _etc._); _narcotic poisons_ affect
only or chiefly the brain (_Agrostemma_, _Papaver_, _Atropa_) or chiefly
the spinal cord (_Claviceps purpurea_, _Lolium temulentum_);
_acrid-narcotic poisons_ induce to a greater or less extent the symptoms
of both the foregoing groups (_Taxus_, _Colchicum_, _Cicuta_, _Solanum_,
_etc._).
(3) As the accounts of the individual plants will show, the toxic
principles of many plants are not yet well understood, either as regards
chemical constitution or symptoms caused. Many poisons may be driven off
by heat (boiling, drying), and some plants may thus be rendered
harmless.
Most of the toxic principles of our native poisonous plants are
Alkaloids or Glucosides. The former all contain nitrogen, differ
considerably in molecular constitution, and are usually combined with
widely distributed organic acids. In the pure state they are colourless
and usually stable, crystalline or amorphous solids, or readily volatile
liquids; they usually have a burning taste. In general the same base is
confined to species of the same order—_e.g._ Solanine to the
_Solanaceæ_. The alkaloids include the most powerful poisons.
The term “Glucoside” indicates a group of substances which by the action
of an acid or enzyme are split up into a sugar (grape sugar, galactose
or rhamnose) and other substances (alcohol, aldehydes, acids). They have
a bitter taste and are generally readily soluble in water. Related to
the glucosides are also the Saponins, remarkable for the fact that they
induce an exceedingly frothy condition in water; the prussic acid
yielding compounds or cyanogenetic glucosides (_e.g._ Amygdalin and
Phaseolunatin) also belong to this group. Other substances will be
mentioned in the succeeding chapters.