The symptoms in the horse are dilatation of pupils, vertigo, uncertain gait, and trembling. The animal falls, the body is cold and the extremities are stiff, respiration is laboured, the pulse is slow and small, and there are convulsive movements of the head and limbs. There is rapid enfeeblement, and death may occur within thirty hours.
In pigs, foaming, convulsions and paralysis have been observed; the stomach and intestines were inflamed and the lungs congested.
REFERENCES.
[4], [16], [73], [81], [106], [128], [130], [141], [190], [203], [204],
[205], [213], [233], [235], [254].
EQUISETACEÆ.
Horsetails (Equisetum sp.). A very great deal has been written on the subject of Equisetosis or Equisetum poisoning, and even at the present day opinion is divided as to which species are poisonous and to what extent. From the time of Linnæus there has been uncertainty as to the species, which has generally been given as E. arvense. Two German papers, by Weber and Lohmann respectively, published by the German Agricultural Society in 1903 and 1904, have done much to remove doubt on the matter, but cannot be said to have settled the question absolutely. These two papers seem to have been overlooked by some recent writers on the subject, but Lohmann’s appears to be the most authoritative paper yet written. Both are referred to below.
It seems to be definitely proved that certain species of Equisetum really are poisonous, hesitating statements notwithstanding. Chesnut and Wilcox state that there are cases of poisoning of both horses and sheep by E. arvense in the United States, though they are not common, and the opinion is expressed that “the plant, if deleterious, is evidently so only on account of its harsh scouring action in the mouth and intestinal tract.” On the other hand Rich and Jones record poisoning of horses by E. arvense in hay, but while adding that horses seem to develop a depraved appetite for the weed, they state that they have no evidence that horses grazing upon the green plant are poisoned. Güssow’s experience has been that cattle do not suffer any inconvenience at all from this species, or only very slight disturbance of the digestive organs, but that horses are conspicuously subject to fatal poisoning by it. Examination of hay on which a considerable number of poisoned horses were fed revealed in every case the presence of E. arvense. When the food was changed, horses, if not too seriously affected, made rapid recovery. (Treatment suggested is to change to easily digested food, give a sharp purgative, and follow by small doses of nux vomica three times a day.) Pammel says that in recent years a disease of horses in Vermont has been attributed to hay and fodder containing the weed; that it is proved by experiment that when ingested in sufficient quantity E. arvense is capable of causing fatal poisoning in horses, and is at times the cause of extensive losses; and that young horses are most susceptible, while grain-fed horses are less susceptible than others. He adds that sheep are supposed to be slightly affected, but cattle eat hay in which it occurs in large proportion with impunity.
Coming to the two German reports, it is stated by Weber (1903) that E. palustre contains a specific poison for cattle and other ruminants, but sheep and goats are able, owing to their fine muzzles, to separate it in fodder, and hence suffer less. Horses and pigs, he says, seem to suffer very little. Young animals and stock, from districts where the species does not occur, suffer more than those from places where it occurs—the latter appearing to learn early to avoid it.
Lohmann conducted feeding experiments with guinea-pigs with E. arvense, E. palustre, E. pratense, E. sylvaticum, E. maximum, and E. heleocharis (not British). He also fed E. arvense and E. palustre to horses, cattle, sheep, pigs, and geese in considerable quantities for many days on end; and made experiments with aconitic acid on guinea-pigs and horses. The feeding experiments with guinea-pigs showed that of the species named only E. palustre and to a less extent E. sylvaticum are poisonous plants (to guinea-pigs). With the large domestic animals the experiments showed E. arvense to be a harmless plant, and E. palustre to be really injurious to cattle but avoided by other stock. Lohmann considers that the many statements in the literature agree in part with this result, and that the divergent observations may be traced to various causes, among which perhaps an abnormal chemical composition of the weed fed plays a principal part.