Objectionable Characteristics of Range Plants 
W. F. MUEGGLER? 
The significance of objectionable character- 
istics in range plants is twofold. They may 
cause a direct loss in animal products by poi- 
soning or otherwise injuring livestock, or they 
may simply reduce the production of usable 
forage. Toxic properties are naturally of great 
concern because of the occasional dramatic 
livestock losses that have occurred in the past, 
and because of the careful management re- 
quired to prevent such losses. To a much lesser 
degree, some species are mechanically inju- 
rious to livestock because of peculiar struc- 
tural features. These seldom cause death, but 
can cause condition loss or prevent forage utili- 
zation. Still less obvious are the effects of cer- 
tain physiological and morphological charac- 
teristics of range plants. These affect livestock 
only indirectly by altering both the quantity 
and quality of forage available for use. 
Though direct loss from poisoning is most 
spectacular, the loss in production of usable 
forage is probably of much greater economic 
significance. Plants with objectionable features 
simply occupy space and utilize moisture and 
nutrients that could more profitably be used by 
valuable forage plants. They reduce the graz- 
ing capacity of the range. 
We often tend to classify plant characteris- 
tics as either good or bad, but nature is not 
that simple. With few exceptions, we find that 
objectionable features have highly variable ef- 
fects—they differ both with kind of livestock 
and with conditions under which the features 
are encountered. Under certain conditions some 
range plants can be very harmful; under dif- 
ferent conditions these same species provide 
valuable forage. 
For convenience, the discussion of objection- 
able characteristics is divided as follows: 
Chemical constituents, structural features, and 
physiological attributes. The first two can be 
further divided into those factors which di- 
rectly damage livestock in some way, and those 
which simply discourage use of what might 
otherwise be valuable forage. 
CHEMICAL CONSTITUENTS 
Poisons 
The purpose here is not to list all of the 
range plants potentially poisonous to livestock. 
*The author is Principal Plant Ecologist at the 
Forestry Sciences Laboratory, Bozeman, Mont. The lab- 
oratory is maintained in cooperation with Montana 
State University. The laboratory is under the jurisdic- 
tion of the Intermountain Forest and Range Experi- 
ment Station. Headquarters for the station is at Ogden, 
tah. 
This information can be found in numerous 
U.S. Department of Agriculture and State Ag- 
ricultural Experiment Station publications. 
Rather, the major groups of chemical constitu- 
ents that have been found in toxic quantities in 
range plants will be pointed out and examples 
will be given of plants in which they occur. 
Much of the information on toxins was ob- 
tained from Kingsbury’s textbook (1964) in 
which he discusses all of the known poisonous 
plants in the United States and Canada. 
Glycosides (Glucosides) 
Many glycosides are nontoxic, whereas oth- 
ers are very toxic. They include the most 
widely distributed toxins found in plants. The 
most prominent toxic glycosides include the 
cyanogenics, irritant oils, coumarins, and the 
saponins. 
Of the numerous glycosides, perhaps the 
cyanogenics cause the most poisoning of live- 
stock. Though the glycoside itself is harmless, 
highly toxic hydrocyanic acid (HCN) is 
formed by hydrolysis. Hydrolysis can occur in 
either the plant or in the animal. Frequently, 
HCN forms in the plant when growth is 
stunted by wilting or frosting. HCN forms 
more readily in ruminant than in nonruminant 
animals; the microflora in the rumen promotes 
the enzymatic action that leads to hydrolysis. 
Death usually is rapid, occurring within a few 
hours. 
The cyanogenic glycoside content of given 
plants varies with such environmental condi- 
tions as stage of growth, rainfall, fertilization, 
and general climate. Both speed of ingestion 
and speed of hydrolysis are important in deter- 
mining whether poisoning will occur. The 
cyanide in HCN is highly reactive and capable 
of entering chemical changes that will prevent 
absorption. It is also readily excreted. The 
amount of nontoxic material in the digestive 
tract and the degree of wetness are important 
as dilutants to the cyanide. 
Among the most valuable range plants con- 
taining cyanogenic glycosides are Triglochin 
maritima and T. palustris. These occur 
throughout the United States on marshy sites, 
but are usually poisonous only when growth is 
stunted by drought. Various Sorghum spp., 
often used as forage crops, cause livestock 
losses in the Central and Southern States, 
especially following drought or frost. HCN 
poisoning has occurred, particularly from use 
of S. vulgare and S. halepense. The sometimes 
poisonous properties of Prunus spp. are also 
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