244 STOCK-POISONING PLANTS AND THEIR CONTROL 



and hence some plants known to be poisonous may never cause 

 symptoms of distress in certain animals. 



Poisonous plants are not generally grazed as a matter of choice. 

 Accordingly there is a striking relation between scarcity of food 

 and losses by poisonous plants.^ The heaviest losses are most 

 ^^^able to occur on ranges that are badly depleted. On such 

 areas the more palatable species produce a weak growth, whereas 

 the poisonous plants, being ordinarily cropped ^but Httle, start 

 growth in advance of the choice forage and may constitute a 

 conspicuous part of the early spring vegetation. Not uncom- 

 monly livestock losses are heavy on lands which are grazed pre- 

 maturely. Moreover, vegetation of all kinds is less nutritious 

 early in the spring than later in the season, and this fact tends 

 to widen the selection of leafage consumed by livestock, thus in- 

 creasing the consumption of poisonous plants. Such overgrazed 

 areas should be re vegetated as soon as possible. They should 

 not be grazed too early in the season, and care should be taken 

 not to stock them too heavily. 



Range Use and Variation in Poisonous Substances of Plants. — 

 It is well known that alkaloids and other toxic substances are 

 not uniformly distributed throughout the tissues of all poisonous 

 plants. 



In the toxic lupines poisoning is unknown until the seed pods 

 are well formed; therefore, practically all lupine poisoning occurs 

 in late summer and in the autumn. Accordingly, lupine- 

 infested lands should either be grazed early in the season, before 

 the seeds have developed, or late in the autumn after the seeds 

 have dropped. Although the lupine pods are poisonous, they 

 do not cause deaths unless eaten in large quantities. Sheep are 

 especially subject to lupine poisoning and therefore should not be 

 grazed on lupine areas when the pods contain seed. 



The root of the water hemlock contains more deadly toxic 

 properties than do the leaves or stem. Sheep seldom trample 

 out the tubers of this plant, whereas cattle are more hable to do 

 so, and therefore are subject to greater loss from eating them. 



^ Marsh, C. Dwight, " Prevention of Losses of Live Stock from Plant Poisoning." 

 U. S. Dept. of Agr. Farmers Bui. 720, 191 6. 



