This section is from the book "A Guide To The Poisonous Plants And Weed Seeds Of Canada And The Northern United States", by Robert Boyd Thomson, H. B. Sifton. Also available from Amazon: A guide to the poisonous plants and weed seeds of Canada and the northern United States.
Oxytropis spp. DC, also known as Aragallus.
Other Common Names: Loco Weed, Crazy Weed, Loco Vetch, White Loco.
For many years stockmen of the west have been suffering great losses from the disease known as "Loco." Several agencies have at various times been held responsible for the trouble. One opinion was that animals not regularly supplied with salt acquired the disease from eating the alkali so common in certain soils of the plains. This idea has been shown to be erroneous since cases of "locoing" have become known on ranges where the alkali could not be obtained. Various plants were also blamed for the trouble and investigation has proved that this is correct, there being now several distinct species of recognized Loco weed.
The disease takes a peculiar course, not unlike the development of the drug habit in human beings. Horses and sheep are the animals usually affected, but cattle also become locoed in some cases. Animals may be pastured for years on ranges where the Loco Weed is found and show no ill effects, as they ordinarily avoid it. When one of them acquires the taste, however, it develops a craving for the weed and hunts it incessantly. Sheep acquire the habit by imitation, and so it is important to remove all locoed animals at once from the flock.
In chronic cases of locoism an immunity is developed, so that increasing quantities are necessary to produce characteristic symptoms. In such cases there is a continual craving for Loco Weed, the animal nervously searching it out and feeding on it. Locoed sheep become more and more emaciated and the fleece drops out in patches. There is an uncertainty and incoordination of the muscular movements, comparable to that exhibited in cases of drunkenness. The animal wanders aimlessly about, straying from the flock. Sight and hearing are affected. In some cases complete blindness ensues, and in others the animal is unable to judge the size of objects, or its distance from them. In later stages fits of trembling follow each other at short intervals and the power of locomotion is gradually lost. Death comes from exhaustion and lack of nutrition.
Fig. 12. - Stemless Loco Weed - Oxytropis Lamberti.
Cattle and horses sometimes become dangerous. Cattle have been known to attack persons or other animals. Locoed horses may work as usual for some time and then develop vicious fits of kicking. Their lack of judgment of the distance and size of objects is often very marked. They become easily frightened at imaginary objects and run away. As is the case with sheep, they become stupid and lethargic as the disease progresses. Chesnut and Wilcox tell of one horse that spent two weeks without moving from a spot of dry ground one hundred and fifty feet square. The horse then walked some distance to a stream and in attempting to drink, fell and was unable to rise.
When a large quantity of the weed is eaten by an animal unused to it, acute poisoning results. The symptoms are much more violent than in chronic cases. In a case described by Chesnut and Wilcox the animal, a sheep, was completely blind within ten hours after she was first observed eating Loco Weed. She exhibited locomotor ataxia, walking in circles with her head bent to the right. As the disease progressed the circles became smaller. Pronounced muscular twitchings were observed and forcible grinding of the jaws, these symptoms preceding a spell of walking. The pulse, at first irregular, became normal on the second day, and later very rapid and weak. Respiration also became progressively more rapid during the course of the disease. Death occurred on the morning of the fourth day, after a period characterized by muscular twitchings and inability to stand.
No satisfactory cure has been found for loco disease. Sheep that have acquired the habit, if taken in time, may be removed from Loco-infested areas and converted into mutton by the use of plentiful feed of a succulent nature. They should never be returned to the range, however, as they will at once begin again to eat the Loco. Horses that have been affected are never safe afterward, becoming frightened or vicious at most unexpected times.
Hundreds of thousands of dollars have been spent in attempts to rid the sheep ranges of Loco Weeds, but the results have been unsatisfactory. If care is taken to remove at once any sheep that has become locoed, no great losses will occur. One experienced sheepman is said by Chesnut and Wilcox to have lost so many sheep from Loco Weed that he decided not to continue the business. He sold his ranch to a stranger, who stocked it with sheep from another part of the country and had no trouble. The new flock contained no locoed animals from which the healthy ones could learn the habit.
There are thirty-four species of Oxytropis listed from western North America and of these twelve are reported from parts of Canada. Several have been proved poisonous, the one most commonly blamed being Oxytropis Lamberti Pursh. All species with the exception of two, O. deflexa (Pall.) D C, and O. foliolosa Hook., are acaulescent, i.e., lack stems and have leaves and flower-stalks growing in tufts from the root-crowns. The whole plant, including the leaflets of the pinnately compound leaves, is covered with numerous whitish hairs. The flowers are of the legume type, ranging from yellowish white to blue and brilliant purple,
Fig. 13. - Flower of Stemless Loco Weed, showing "spur" (centre right), on the keel.
and borne in spikes or narrow racemes. They are distinguished from those of the closely related genus Astragalus by the presence of a spur-like point, one-eighth inch long, at the tip of the keel. The flowering season is June and July and it is at this time that the plant is eaten most freely, though animals that have acquired the habit will search out and eat the fruiting plants.