Diseases of cattle, sheep, goats and swine

by G. Moussu; Jno. A. W. Dollar

Fig. 92.—Woolly loco weed (Astragalus mollissimus). a, Whole plant; b, section of pod—both one-third natural size.

This is an erect tufted perennial, 4 to 18 inches high, with pinnately divided leaves and spikes of white or cream-coloured flowers, shaped like those of the pea. The pod is one-celled, and when shaken produces a rattling sound, which gives the plant the name of “rattle weed” in some localities. The white loco weed is exceedingly common throughout Montana. It occurs most abundantly on the northern slopes of foothills up to an altitude of about 8,000 feet. Its preferred habitat is for the most part in rather dry situations. The habit of the plant varies in different parts of Montana. In some localities the flowers are pure white, while in others they are decidedly yellow.

In Colorado the plant which is most ordinarily known as loco weed is Astragalus mollissimus, while in Montana the species already named is perhaps most important; but there are others which have a rather wide distribution and are known to produce the same effects. Among these may be mentioned A. splendens, A. lagopus, and A. besseyi.

The losses caused from the loco disease are very heavy in nearly all the Rocky Mountain States. The locoed condition is so commonly observed among sheep and horses that cases are not reported, and it is practically impossible to learn the exact extent of the disease. In the Judith Basin one prominent stockman was nearly ruined financially by the prevalence for a number of years of the loco habit among his sheep. In another instance the raising of horses was abandoned over a large tract of country on account of the loco weeds.

The loco disease occurs under two forms—an acute and a chronic. An acute case of loco disease was observed by Dr. Wilcox in a two-year-old ewe with a lamb at its side. The ewe was observed eating large quantities of white loco weed on May 22nd, 1900. During the afternoon of the same day it became unmanageable, and the lamb was badly affected. An examination of the ewe at this time showed that it was completely blind and was affected with dizziness. It walked around in long circles to the right, and after a short period remained standing for a few moments in a sort of stupor. At the beginning of each attack the head was elevated and drawn to the right; eyelids, lips, and jaws were moved rapidly. Each attack lasted from one to two minutes and the intervals between the attacks lasted about five minutes. The second day the attacks became more severe and of longer duration, the head being turned more decidedly to the right and the animal sometimes falling upon the ground. Similar symptoms, accompanied by digestive disturbances, were manifested by the lamb during the second day, and it died during the afternoon. On the morning of the third day it was found that the ewe was pushing against the fold, and had apparently been in that position during the greater portion of the night. The animal then began to whirl round to the right. Later it became unable to stand, and the spasmodic movements were largely confined to the legs. On the morning of the fourth day it died. The pupil of the eye was at no time dilated, and the expression was nearly normal. The pulse was at first very irregular, but on the second day became again regular and of normal frequency. The only remedy which was tried was frequent injections of one-quarter grain doses of morphine, but this was without effect. Two other ewes ate smaller quantities of loco weed at the same time and were similarly affected, but less severely. In these cases morphine was tried with better success. The lambs, however, died from the poisonous properties contained in the milk of the mother.

The general symptoms of loco disease are quite familiar to all stock raisers. Perhaps the most characteristic are those of cerebral origin, and are shown in peculiarities of gait and action, which may be compared to a drunken condition. The brain disturbances may consist in impairment of the special senses or in irregular motor impulses, which produce incoherent muscular action. In some cases the animal becomes blind. More frequently the animal makes errors in judgment of the size and distance of objects. These visual disturbances are often quite ludicrous. The animal often takes fright, apparently at imaginary objects, or at objects which under ordinary circumstances would cause no alarm. Locoed horses are somewhat dangerous for driving purposes on account of their tendency to run away. Such horses are frequently attacked with kicking fits without any apparent cause. The sense of hearing is often affected, and the response to sounds is irregular and out of proportion to the volume and character of the sound. Irregularities in muscular movements of sheep may assume a variety of forms. The animal may simply carry its head in an extended or otherwise unnatural condition. In some cases the back is arched. Trembling is a characteristic symptom. In locoed horses a great difficulty is sometimes experienced in persuading them to go backward. Locoed sheep are exceedingly difficult to manage. The different members of the flock may suddenly take a notion to run away in different directions, with the result that it is almost impossible for the shepherd to prevent their becoming separated. In cattle the disease appears to be rare, although symptoms, so far as observed, are essentially the same as those in sheep and horses. Occasionally locoed cattle manifest dangerous symptoms, and attack men and other animals.

In chronic cases of loco the animal gradually becomes more emaciated and crazy. In sheep the fleece may be shed in patches or as a whole. The animal becomes unable to care for itself, and is apt to fall into the water while attempting to drink. Fits of trembling are of frequent occurrence, and the animal finally dies of inadequate nutrition and total exhaustion. In chronic cases of loco disease in horses the animal is usually left to its own resources on the range. During the later stages it may remain for weeks at a time upon a small area of ground without taking water. Dr. Wilcox saw a number of such cases in horses that were almost unable to walk. Under such circumstances the animals seldom or never lie down. One horse which was seen remained for a period of two weeks, in 1897, upon a piece of ground about 150 feet square. During this time the horse had no water.

Numerous autopsies on locoed sheep and horses revealed slight congestion of the brain membranes in all cases. The lungs and heart were in normal condition. Fatty tissue was considerably reduced in quantity, and the muscles were paler in colour than under normal conditions.

The most serious mistake in connection with loco disease is made in allowing locoed sheep to remain with the rest of the flock. The loco habit is apparently learned by imitation of locoed animals, and so long as locoed sheep are allowed to remain with other sheep the loco habit rapidly spreads. An experienced sheep raiser, after being nearly ruined financially through the loco disease, adopted the method of immediate isolation and the feeding of locoed sheep for mutton. His stock was replaced with sheep that were free from the loco habit, and the trouble has been entirely eradicated from his range.