W29 

 (leaf 2) 



that the only conditions under which poisoning from this plant may 

 occur are those where the stock are very hungry and there is an 

 absolute lack of other feed." Thus, the greatest losses have resulted 

 along trails or driveways and on depleted bedgrounds, pastures, and 

 ranges where the livestock were forced to eat the plant, due to lack 

 of other forage. 



Horsetail milkweed is so virulent that relatively small quantities 

 may cause severe sickness, or even death. Marsh 2 states that 6^/2 

 pounds of the green vegetation ordinarily is sufficient to kill a 1,000- 

 pound steer; iy 2 pounds, a 1,000-pound horse; and 2% ounces, an 

 average-sized sheep. The plant is, therefore, most toxic to sheep, 

 less so to horses, and considerably less poisonous to cattle; with 

 largest losses among sheep. Poisoning of horses seldom happens, as 

 those animals are very discriminatory concerning their feed. Occa- 

 sionally reports, probably authentic, are heard that this species has 

 caused goat losses. The plant appears to remain rather uniformly 

 toxic during the entire season; the leaves are much more virulently 

 poisonous than the steins. Chemical analyses show that horsetail 

 milkweed contains several poisonous substances, but the symptoms of 

 range poisoning are believed due to a resinlike substance which can 

 be extracted from the plant by use of cold alcohol. 3 



Animals poisoned by horsetail milkweed display very character- 

 istic symptoms, such as loss of muscular control from about 2% to 

 21 hours after grazing the plant. Affected animals stagger and 

 wobble, especially in the hind legs, soon fall, and make strenuous 

 but futile efforts to rise. In severe cases violent spasms follow, in 

 which the prostrate animal outstretched on one side throws its head 

 back and forth, and makes running movements with its legs. Under 

 range conditions, the animals have even been observed beating their 

 heads violently upon the ground. 3 Marsh and coworkers (op. cit.) 

 further report that the poisoned animals bloat markedly, abdominal 

 gas accumulating rapidly; the respiration is labored, and the pulse 

 is both rapid and weak. In fatal cases, the spasms decrease in in- 

 tensity before death, which results from, respiratory paralysis. Body 

 temperatures sometimes increase to over 110 F. during the sickness. 

 Post-mortem examinations indicate that the outstanding effects of 

 horsetail milkweed poison, besides the accumulation of gas, include 

 lesions of the kidneys and central nervous system. 3 The poison 

 apparently is not cumulative, since sickness or death do not result 

 unless sufficient herbage either to prove toxic or kill the animal is 

 eaten at one time. This plant, in certain far- western poisonous-plant 

 literature, has been mistakenly referred to the more eastern, whorled 

 milkweed (A. verticillata) ; the latter is a species of the Atlantic 

 Plains and the Mississippi Valley, and apparently does not grow in 

 the Rocky Mountains or farther west. 



2 Marsh. C. D. PLANTS POISONOUS TO SHEEP. in. THE WHORLED MILKWEED. Natl. 

 Wool Grower 18 (10) : 25-26, illus. 1928. 



8 Marsh, C. D., Clawson, A. B., Couch, J. F., and Eggleston, W. W. THE WHORLED 



MILKWEED (ASCLEPIAS GALIOIDES) AS A POISONOUS PLANT. U. S. Dept. Agr. Bull. 800, 



40 pp., illus. 1920. 



