Animals must have protein to form new cells 
essential for body maintenance, growth, repro- 
duction, and lactation. The ruminant animal 
needs protein for the rumen micro-organisms 
to effectively digest and metabolize carbohy- 
drates and fats. If protein levels fall below a 
minimum, rumen function becomes severely im- 
paired. However, very high protein levels are 
not only unnecessary, but are inefficient for 
ruminant animals (Kleiber 1959). 
Since crude protein content is significantly 
correlated to digestible protein content, deter- 
mination of the crude protein level of a plant 
can give a reasonably reliable indication of its 
feeding value (Sullivan 1962). 
Crude Fat 
All of the various plant substances soluble in 
ether are included in the term crude fat. Lip- 
ids, plant pigments such as chlorophyll and 
carotene, and certain essential oils are removed 
from the plant in the ether extract (Maynard 
and Loosli 1956). Lipids contain true fats (re- 
serve food material), waxes (cuticular compo- 
nents), and phospholipids (structural mate- 
rials). The true fats are fatty acids esterified 
to form triglycerides (Bonner and Galston 
1952). True fat provides approximately 2.25 
times more energy than carbohydrates and 
proteins, but less than one-half of ether ex- 
tract in plants may be true fat (Sullivan 
1962). Some plants may contain quantities of 
volatile oils which have no feeding value and 
may be harmful to rumen micro-organisms, 
thus impairing rumen functions. The sub- 
stances, called “essential oils” because of their 
odor or essence, give many plants their charac- 
teristic odor or taste. Big sagebrush (Artemisia 
tridentata), noted for its aroma, contains large 
amounts of essential oils (Nagy et al. 1964). 
Ruminants are not dependent upon fat in the 
diet, because fatty acids can be synthesized in 
the rumen from carbohydrates and proteins. 
Dietary fat does, however, provide the most 
economical source of energy; thus, a deficiency 
causes the body to use a less efficient source of 
energy. 
Carbohydrate 
Three-fourths of the dry weight of plants is 
composed of carbohydrates, which include sug- 
ars, starch, cellulose, gums, and related sub- 
stances. Thus, the bulk of the plant material 
eaten by range animals consists of some form 
of carbohydrate. Micro-organisms in the 
rumen break down the carbohydrate constitu- 
ents and produce volatile fatty acids that pro- 
vide most of the energy needed by the animal 
(Anninson and Lewis 1959). The carbohy- 
drates considered in feed analyses are fre- 
2 
quently presented as one or more of the follow- 
ing separate components: 
Nitrogen-free extract (NFE).—The portion 
of the plant known as nitrogen-free extract 
contains most of the more soluble carbohy- 
drates such as glucose, sucrose, maltose, and 
starch, and also some of the less soluble forms 
such as lignin, cellulose, and hemicellulose. 
There is no chemical test for this portion; it is 
calculated as the percentage of the sample re- 
maining after the percentages of ash, crude 
fiber, crude fat, crude protein, and moisture 
are subtracted from 100. The disadvantages of 
this technique as it relates to forage quality 
are discussed under the section—‘‘Chemical 
Analysis Systems.” 
Crude fiber.—The portion of the plant that 
withstands boiling in weak acids and alkalies 
is called crude fiber. Its resistant qualities are 
due to cellulose, hemicellulose, lignins, and 
other relatively indigestible constituents. Gen- 
erally, high crude fiber content in forages indi- 
cates low digestibility by animals. However, 
ruminants are able to digest at least 50 percent 
of the crude fiber of most feeds. A certain 
amount of bulk, which is governed mainly by 
the crude fiber content, is thought necessary in 
the diet of animals to avoid the formation of a 
doughlike mass in the stomach (Maynard and 
Loosli 1956). 
Lignin. —The complex, indigestible sub- 
stances found in cobs, hulls, and the fibrous 
portions of roots, stems, and leaves are called 
lignin. Although the chemical structure re- 
mains uncertain all substances designated as 
lignin are considered to have a common basic 
structure (Maynard and Loosli 1956). Lignin 
has an important influence on the degree of di- 
gestibility of many feeds because the more lig- 
nified cellulose becomes, the less digestible it is 
to ruminants. 
Cellulose. —Cellulose consists of a chain of 
glucose units called a polysaccharide. It is 
little affected by weak acids and _ alkalies, 
nor is it acted upon by enzymes secreted by 
the animal. It can be hydrolyzed by strong 
acids to form glucose. Rumen bacteria can 
break it down to form more soluble carbo- 
hydrates. It often combines with lignin as a 
framework for plants and for a_ protective 
coating of seeds. Cellulose is important nutri- 
tionally because it provides the body with a 
major source of energy. The digestibility of 
cellulose depends on its state of lignification 
(Sullivan 1962). 
Hemicellulose—Hemicellulose consists of a 
group of substances which are much less resis- 
tant to acids and alkalies than cellulose. They 
include polysaccharides such as the pentosans 
and certain hexosans that can be broken down 
into simple sugars and other products by the 
