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 | |||||||
|---|---|---|---|---|---|---|---|
| Fertiliser | Time of Application | Per acre | 1906 3rd year’s plants | 1907 4th year’s plants | 1910 1st year’s plants | 1911 2nd year’s plants | 1912 3rd year’s plants |
| Main crop | 0·54 | 0·34 | 0·61 | 0·59 | 0·68 | ||
| Farmyard manure | March | 50 loads | 0·54 | 0·34 | 0·61 | 0·53 | 0·71 |
| Nitrate | March & April | 2 cwt. | 0·52 | 0·23 | 0·54 | 0·46 | 0·64 |
| Calcium cyanamide | Do. | 1 cwt. | 0·69 | 0·49 | 0·75 | ||
| 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 |