The term loco is of Spanish origin and has come to us through the Spanish speaking residents on the cattle raising plains and the Pacific Coast. The word is defined to mean mad, crazy, foolish. It has been applied indiscriminately to a disease in stock manifested by these symptoms, and to a variety of leguminous plants, found growing on the western lands and supposed to cause the disease in question. The plants complained of are Astragalus Hornii, and A. Lentiginosus (Griesbach) in California, A. Mollissimus (Torrey) and Oxytropis Lamberti (Purshiana) in Colorado and New Mexico. Other allied species, and like these found also in the other Rocky Mountain States, Sophora Serecia, Oxytropis Multifloris, O. Deflexa, Malvastrum Coccinium, and Corydalis Aurea var. Occidentalis have been less confidently charged with producing the disease.
These plants grow on poor, dry, sandy or gravelly soils, and having great power of resisting drought, are often in fair growth, and present an abundant mass of leaves when surrounding vegetation is withered up. Hence, it is alleged, the animals are driven to use it when nothing else is obtainable and once accustomed to it, the desire for more becomes a veritable craze or neurosis, and the victim searches for it and devours it to the exclusion of other food.
The following quotations may serve to illustrate the effects alleged:
Among the symptoms first noticed are loss of flesh, general lassitude and impaired vision; later the animal’s brain seems to be affected; it becomes vicious and unmanageable and rapidly loses both flesh and strength. Frequently when approaching some small object it will leap into the air as if to clear a fence. The patient also totters on its limbs and appears as if crazy. After becoming affected it may linger many months, or a year, but usually dies at last from the effects of the complaint. (Dr. Vasey. Report of Dept. of Agriculture, 1884).
“I think very few if any animals eat the loco at first from choice; but as it resists the drought until other food is scarce they are first starved to it, and after eating it a short time appear to prefer it to anything else. Cows are poisoned by it as well as horses, but it takes more of it to affect them. It is also said to poison sheep. As I have seen its actions on the horse, the first symptom apparently is hallucination. When led or ridden up to some little obstruction, such as a bar or rail lying in the road, he stops short, and if urged, leaps as though it were four feet high. Next he is seized with fits of mania in which he is quite uncontrollable and sometimes dangerous. He rears, sometimes even falling backwards, runs or gives several successive leaps forward, and generally falls. His eyes are rolled upward until only the white can be seen, which is strongly injected and as he sees nothing, is as apt to leap against a wall or a man, as in any other direction. Anything which excites him appears to induce the fits, which, I think, are more apt to occur in crossing water than elsewhere, and the animal sometimes falls so exhausted as to drown in water not over two feet deep. He loses flesh from the first and sometimes presents the appearance of a walking skeleton. In the next and last stage he only goes from the loco to water and back, his gait is feeble and uncertain, his eyes are sunken and have a flat, glassy look, and his coat is rough and lustreless. In general the animal appears to perish from starvation and consequent excitement of the nervous system, but sometimes appears to suffer acute pain, causing him to expend his strength in running wildly from place to place, pausing and rolling, until he falls and dies in a few minutes.” (O. B. Ormsby, Report Dept. of Agriculture, 1874.)
“Animals are not fond of it at first, or don’t seem to be, but after they get accustomed to the taste they are crazy for it and will eat little or nothing else when loco can be had. There seems to be little or no nutrition in it as the animal invariably loses flesh and spirit. Even after eating of it they may live for years, if kept entirely out of its reach, but if not, they almost invariably eat of it until they die.” (Mrs. T. S. Whipple, San Luis, Cal. Report Dept. of Agriculture, 1874).
“Cattle, after having eaten it,” Oxytropis Lamberti, “may linger many months, or for a year or two, but invariably die at last from the effects of it. The animal does not lose flesh apparently, but totters on its limbs and becomes crazy. The sight becomes affected so that the animal has no knowledge of distance, but will make an effort to step over a stream or an obstacle while at a distance off, yet will plunge into it or walk up against it on arriving at it.” (Dr. Moffat, U. S. Army.)
“The term loco, simply meaning foolish, is applied because of the peculiar form of dementia induced in the animals that are in the habit of eating the plant. Whether the animals (horses chiefly) begin to eat the plant from necessity (which is not likely) or from choice, I am unable to say. Certain it is, however, that when once commenced, they continue it, passing through a temporary intoxication, to a complete nervous and muscular wreck in the latter stages, when it has developed into a fully marked disease, which terminates in death from starvation or inability to digest more nourishing food. The animal, toward the last, becomes stupid or wild, or even vicious, or again acting as though attacked with blind staggers.” (Dr. Rothrock, Report of Dept. of Agriculture, 1884).
Dr. Isaac Ott, of Easton, Pa., gives the following as the physiological action of the Astragalus Mollissimus: “It decreases the irritability of the motor nerve, greatly affects the sensory ganglia of the central nervous system, preventing them from readily receiving impressions. Has a spinal tetanic action. It kills mainly by arrest of the heart. Increases the callory secretion. Has a stupifying action on the brain. Reduces the cardiac force and frequency. Temporarily increases arterial tension, but finally decreases it. Greatly dilates the pupil.” (Amer. Jour. of Pharmacy, 1882).
In opposition to these statements Professor Sayre, of Kansas, after an extended observation, arrived at the conclusion that “it is a grave question whether loco weed is a poison at all; upon chemical examination no poisonous principle of any kind was discovered; no toxic effect was observable when administered to frogs, cats, dogs, or the human species, ... the point cannot be accepted as a settled one whether loco is poisonous to cattle or not.”