STOCK-POISONING PLANTS OF THE RANGE. 
27 
milkweeds are abundant, they will eat them for lack of better forage 
and frequently with disastrous results. There is little danger from 
any form of milkweed so long as animals are well fed. 
There is no known 
successful way of treat- 
ing milkweed poison- 
ing, except by preven- 
tion. 
THE COMPOSITE FAM- 
ILY COMPOSITE). 
COCKLE BUR, CLOTBUR 
(SPECIES OF XANTHIUM). 
The cockleburor 
clotbur, shown in Fig- 
ure 25, is represented 
by a number of species 
(Xanthium spp.), is 
very widely distrib- 
uted, and has been the 
cause of losses of cattle 
and swine in many lo- 
calities, especially in 
Fig. 23. — A sheep poisoned by the Great Plains whorled 
milkweed (AscJepias pumila). The weakened condi- 
tion of the hind legs is noticeable, as in the Mexican- 
whorled-rnilkweed case. 
Oklahoma, Texas, and New Mexico. While 
long 
supposed to be 
poisonous, it is only very recently that definite experimental proof 
of its toxic character has been obtained. 
It is said that the burs produce mechanical injury by irritating the 
aliment arv 
matted together to form balls which 
canal or by becoming 
cause intestinal ob- 
struction. It is claimed 
that there have been 
cases of the lodging of 
burs in the throat. 
Some recent authors 
have stated that the 
only injury produced 
by cockleburs is the 
mechanical effect. 
There is now, however, 
positive proof of poi- 
soning of swine, sheep, 
cattle, and chickens. 
There are reports also 
of the poisoning of 
horses. All the poison- 
ing is by the young 
plant in the cotyledon 
stage. Young pigs are 
especially susceptible to the plant and have been lost in great num- 
bers. Figure 26 shows a pig fatally poisoned. While the plant has 
been shown to be poisonous to sheep, there have been no reports of 
losses of sheep under range conditions, but the burs produce trouble 
by becoming tangled in the wool and causing a considerable dockage. 
Fig. 24. — A horse poisoned by the western whorled 
milkweed (Asclepias yulioiiles). The violent convul- 
sions are characteristic of poisoning by the whorled 
milkweeds. 
