metabolism than for all other purposes com- 
bined. Energy is the major basis in the compi- 
lation of diets for humans as well as of rations 
for livestock (Swift 1957). 
With the possible exception of protein and 
phosphorus deficiencies, the most common nu- 
tritional deficiency affecting range animals is 
lack of either available energy, digestible en- 
ergy, or both. Energy shortages may be due to 
insufficient feed, or to low dry-matter content 
in lush, watery feed. Even if abundantly availa- 
ble, low-quality roughage will not supply 
enough total digestible nutrients to meet the 
requirements of ruminants (The National 
Academy of Sciences-National Research Coun- 
cil 1957, 1963). 
A shortage of energy-producing feed is most 
common on overused winter ranges and on 
early spring ranges at the time animals 
switch to watery green grass and forbs. Poor- 
quality winter forage adversely affects range 
animals in several ways: It provides insuffi- 
cient energy; protein, and phosphorus may 
be inadequate for the animal to make efficient 
use of the available energy; and it causes ces- 
sation of growth, loss of weight, reproductive 
failure, and impaired rumen function. Also, 
range animals may eat an excessive quantity of 
watery green forage after spring growth be- 
gins. The result may be scours or inability of 
the weakened animal to adjust to the new 
feed, with consequent heavy mortality. 
Gross energy is the heat given off by a sub- 
stance during complete oxidation or burning. It 
is the starting point in determining the energy 
values of feeds. Energy is usually expressed in 
calories per unit of weight. A measure of gross 
energy is important because it provides a com- 
mon basis for expressing nutritive value. In 
general, fats contain more than twice as much 
energy-producing substances as carbohydrates, 
while proteins have only slightly higher en- 
ergy values than carbohydrates (Maynard and 
Loosli 1956). 
Chemical Analysis Systems 
There are several methods for separating 
plant material into various nutritive com- 
ponents. Some of these methods are discussed 
in this section. 
Proximate Analysis 
The method of proximate analysis was intro- 
duced prior to the 20th century, and is still in 
common use. It involves the determination of 
crude protein, crude fat (ether extract), crude 
fiber, ash by chemical tests and an estimation 
of nitrogen-free extract (by subtraction of the 
percentages of the other components from 
100). The most obvious shortcomings of the 
4 
proximate method are that crude fiber and ni- 
trogen-free extract are not precise chemical 
groups, and that the carbohydrates are not 
necessarily separated into digestible and indi- 
gestible portions (Richards and Reid 1953). 
The nitrogen-free extract portion does not 
have the high digestibility often attributed to 
it because it contains a large share of the lig- 
nin which is not digestible, and some of the 
cellulose which is partially digestible. 
Despite the disadvantages of the nitrogen- 
free extract and crude fiber techniques for de- 
scribing the carbohydrate portion of forages, 
the proximate scheme remains useful. Most 
of the literature in the animal nutrition field is 
based upon it. Until the methods of determin- 
ing other carbohydrate components such as lig- 
nin and cellulose are adopted for routine analy- 
sis, the proximate method will remain in gen- 
eral use (Miller 1961). 
Other Analysis Schemes 
Many studies on the nutritional value of 
plants also present some data on mineral com- 
position—usually, at least, percentages of cal- 
cium and phosphorus. Instead of crude fiber 
and nitrogen-free extract, some authors list 
percentages of individual carbohydrate com- 
ponents, including cellulose, hemicellulose, 
starch, reducing and total sugars, and lignin. 
One of the newer methods to replace the 
crude fiber and nitrogen-free extract portion of 
the proximate scheme is to determine the lig- 
nin and cellulose content of forages. Many au- 
thors have found a highly significant negative 
correlation between lignin percentages and the 
digestibility of both dry matter and organic 
matter. There is a high negative correlation 
between lignin content and digestible energy, 
digestible cellulose, and digestible protein 
(Sullivan 1962). 
The technique of Ellis et al. (1946) can be 
used to determine lignin and cellulose content. 
It is based on the insolubility of lignin and the 
solubility of cellulose in 72 percent sulfuric 
acid. This lignin method has several serious 
disadvantages: (1) Lignin is difficult to deter- 
mine chemically, (2) its exact chemical struc- 
ture is not known, and (3) routine tests for 
lignin are not standardized. 
Van Soest (1966) proposes the determina- 
tion of cell wall residues to replace the crude 
fiber technique. These residues can be consid- 
ered chemical components of feedstuffs that 
cannot be completely digested. Cell wall con- 
stituents of plants can be separated into com- 
ponents that are: (1) Insoluble in a neutral de- 
tergent solution (attached protein), (2) soluble 
in an acid detergent solution (hemicellulose), 
and (3) insoluble in an acid detergent solution 
(lignin, lignified nitrogen compounds, keratin, 
and silica). The cell contents, such as lipids, 
