CONIFERÆ.
The only Conifer which commonly causes poisoning of live-stock is the Yew, but injury might more frequently occur were it not for the fact that Conifers generally are unpleasant to the taste, and are hence avoided by stock. Many species, however, contain Tannin, Resins and Gums, Volatile Oils, and an acrid substance which may cause inflammation of the digestive and urinary tracts, while Tanret found in the young shoots of Picea the bitter glucoside Picein (C14H18O7H2O); Kawalier and Thal found the intensely bitter glucoside Pinipicrin (C22H36O11) in Pinus sylvestris, Thuja occidentalis and Juniperus Sabina; and Kubel isolated Coniferin or Abietin (C16H22O8), a slightly bitter glucoside found in Abies excelsa, A. pectinata, Pinus strobus, Larix europæa and other conifers. It is not clear, however, whether these substances are at all poisonous. It is quite possible that if eaten in quantity the foliage of some Conifers may induce poisonous symptoms and even death in the animals concerned. It is noteworthy, however, that according to Pott the needles of Picea excelsa, Abies pectinata, Larix europæa, and Pinus sp. are, in the mountainous districts of Steiermark, Kärnten, and Tyrol, extensively fed to cattle and sheep, usually as a supplementary food, either fresh or dried and ground up—chiefly perhaps as an appetiser, and in small quantities as a dietetic; Juniperus sp. are similarly utilised in some districts. It is not known to what extent the foliage may be fed without harmful consequences, but Pott states that large quantities can cause hæmaturia and similar effects, and hence only small quantities should be used, and even so may impart a bad flavour to the milk of cows. All green needles frequently cause digestive troubles.
A case has recently (January, 1916) been reported to the author in which a Douglas Fir was cut down and a small branch about 4 ft. long was flung over into a field. Two sheep nipped off the bark and nearly died, but both vomited and recovered. The farmer reporting this experience recalls that over 30 years ago, after a gale, a lot of trees were blown down in a small plantation, and in severe weather the sheep ate the bark to such an extent that 80 of them aborted, while of the ewes which did not eat the bark none aborted, so that it would appear that the bark of Scotch Fir and Spruce was to blame for the loss.
The foliage of the Yew (see below) is well known to be dangerously poisonous to stock, and has caused many losses.
In regard to Cupressus the only cases of poisoning which have been traced are recorded in The Journal of the Board of Agriculture (October, 1905). These cases were reported as follows:—
“Two instances have recently come before the Board in which the death of cattle has been attributed to the poisonous effects of Cupressus macrocarpa and C. nootkatensis. In one case four bullocks died, and on the internal organs being forwarded by the owner to the Royal Veterinary College, Professor McFadyean reported that from the inflamed condition of the fourth stomach and from the description of the symptoms he had little doubt that the cause of death was irritant poison. Some pieces of Cupressus macrocarpa were found in their stomachs, and in default of any other explanation it was suggested that this plant might have some poisonous properties.
“In another case three heifers are stated to have suffered from irritant poison; one of them died, but the other two recovered on removal to another field. The veterinary surgeon in this case also attributed the death to a Cupressus (C. nootkatensis) growing by the side of the field.
“The Board have no information as to the poisonous properties of these two species, nor can any record be found of any similar case which would tend to confirm the suspicion that they are poisonous to cattle.”
REFERENCES.
[4], [16], [76], [144], [213], [252].
Yew (Taxus baccata L.). As stated above, the Yew is the only British conifer that is likely to prove seriously poisonous to live stock. It has unfortunately caused the death of many horses and cattle, while asses, mules, deer, pigs, rabbits, and pheasants have also been poisoned. Many cases of fatal human poisoning have also occurred. For example, the poisoning of a horse, and of cattle, horses, and deer were mentioned respectively in 1885 and 1893 (Jour. Roy. Agric. Soc.). “Through eating the poisonous leaves of a Yew tree, four cross-bred cattle were found dead in a shrubbery at Elmswell, near Driffield” (Daily Mail, 13th Dec., 1913). Many cases of poisoning and death of animals due to eating the foliage direct from the trees have been recorded in the veterinary journals—e.g. the death of 15 cattle in The Veterinary News, 7th Dec., 1912. Tegetmeier recorded the death of pheasants due to Yew leaves and seeds (The Field, 11th Nov., 1893). On the other hand many cases have been recorded in which fatal results have not followed the ingestion of the leaves, and it appears that the lower branches of Yew trees in parks are constantly cropped by cattle without ill effects. (Trans. Chem. Soc., 1902; Jour. Bd. Agric., 1903).
The bark, leaves, and seeds are all poisonous, the leaves usually being the parts eaten. Henslow states that of 32 cases of Yew poisoning 9 were due to the berries and the remainder to the leaves, while 20 of the 32 cases were fatal. In 1879 R. Modlen published a circumstantial account of children poisoned at Oxford by the fruits, and demonstrated that the arillus or scarlet mucilaginous cup surrounding the ripe seed is not poisonous, but that the seeds are so. Apart from idiosyncrasy of appetite stock are perhaps more likely to eat the dark green foliage of the Yew in winter or during scarcity of green fodder than at other times. The old leaves or shoots are the most poisonous parts.
By experiments with autumn and winter leaves Cornevin found that the following quantities would be necessary to kill various animals:—
| Horse | 0·2 | lb. | per 100 lb. live weight. |
| Ass and Mule | 0·16 | lb. | „ „ |
| Cow and Sheep | 1·0 | lb. | „ „ |
| Goat | 1·2 | lb. | „ „ |
| Pig | 0·3 | lb. | „ „ |
| Rabbit | 2·0 | lb. | „ „ |
Other authorities, however, quote much lower quantities as necessary to kill the horse and ox, and Pott says that in the case of horses 150 to 180 grammes (0·33 to 0·4 lb.) is sufficient to cause death in one-quarter to one-half an hour, without previous symptoms. Eaten by an animal on a full stomach a small quantity of Yew may cause little or no dangerous results.
Toxic Principle. The researches of Marmé pointed to the alkaloid Taxine (C37H52NO10) as the toxic substance. Later investigations of Thorpe and Stubbs confirmed this view, and it is generally agreed that this substance is the toxic principle, though doubts as to its being the only poison have been expressed. Taxine has a bitter taste, is a heart depressant, and may cause death from suffocation. The yew also contains a considerable quantity of Formic Acid, and the acrid, irritant volatile Oil of Yew.
Thorpe and Stubbs (Trans. Chem. Soc., 1902) found in the fresh leaves of the common Yew from 0·1 to 0·18 per cent. of Taxine. In an investigation of the Irish Yew (T. baccata var. fastigiata) Moss found Taxine present as follows:—
| Leaves from female tree, fresh | 0·596 | per cent. |
| Leaves from female tree, fresh | 0·623 | „ |
| Seeds from fruit of same tree | 0·079 | „ |
| Another female tree—leaves | 0·323 | „ |
| Another female tree—seeds | 0·082 | „ |
In the leaves of the male common Yew Moss found 0·082 per cent. of Taxine, or less than one-half the quantity found by Thorpe and Stubbs.
Symptoms. The Yew is irritant and narcotic, and the poison is not cumulative, but on the other hand rapidly effective, so that animals may die apparently suddenly, no previous symptoms having been observed.
When small quantities only have been taken the closest attention is necessary to discern the symptoms, which simply consist in a little excitement with a slight rise in temperature.
With larger (but not fatal) quantities the first symptom, excitement, is more pronounced and is followed by nausea, and (where possible) vomiting. There is a pronounced slackening of respiration and circulation, the pulse being small, slow, and difficult to perceive, and the movement of the flanks very slow; sensibility is diminished. There is a fall in temperature, the skin and extremities being cold. The head is lowered, the eyes are closed and there is decubitus. In some cases pregnant animals have aborted. In the horse there are muscular tremors and frequent urination. In cattle and sheep rumination is suspended and there is more or less pronounced tympanites, with eructation, nausea, and sometimes vomiting. Pigs bury the head in the litter and sleep, their sleep being interrupted from time to time by nausea and groaning; or the animals rise, stagger about, and lie down again.
With fatal quantities the foregoing symptoms may be followed by coma, with death in two hours or more after the poisoning, but more generally and usually in horses, asses, and mules (but also in cattle) there is no period of coma, the excitement is less pronounced and often unobserved, and death appears very sudden. The animals stop, shake their heads, respiration is modified, there is falling, and death (sometimes with convulsions) results from cessation of the heart’s action (Cornevin).
The symptoms given by Müller are roaring, torpidity, stupefaction, laboured breathing, convulsions and death in from ten minutes to an hour in the worst cases; or where the course of poisoning is slower, there is salivation, nausea, vomiting, bloating, retardation of pulse and respiration, great giddiness and stupefaction, diabetes and hæmaturia.
The rapidity of the poisoning is confirmed by cases noted in the veterinary journals. Lander shows that the effects often only appear in cattle when chewing the cud; whilst quietly chewing, they drop as if shot. In some examples the animal died while eating the plant, or was found to have fallen and died suddenly and without evidence of a struggle. The animal in some cases will stop suddenly whilst working, start blowing and trembling, stagger, fall on its haunches, then on its side, and die quietly. Death occurs in about five minutes with symptoms resembling apoplexy. A colt died after 16 or 17 hours; the plant was taken on a full stomach, but paralysis of the alimentary system with stoppage of digestion immediately ensued.
In the case of pheasants there was acute inflammation of the small intestines (Tegetmeier).
REFERENCES.
[4], [16], [49], [73], [81], [84], [100], [128], [130], [141], [144], [161],