termine its digestibility. Several approaches 
have been tried. 
Plants have been hand plucked or clipped to 
provide duplicates of vegetation foraged by 
tame herbivores or very tractable wild ani- 
mals. 
Hand harvesting provides a first approxima- 
tion of food quality selected by animals, but 
such plucked samples frequently vary from 
forage samples collected through esophageal 
fistulas. Hand-plucked samples are often of 
lower protein content and higher fiber content 
(Bohman and Lesperance 1967). 
The nutrient and forage composition of in- 
gested food has been determined through the 
use of rumen fistulas in range animals. Rumen 
fistulas are relatively easy to establish and to 
maintain in domestic animals, and these have 
been placed in deer several times. Prior to 
grazing, the animal’s rumen-reticulum is 
emptied through the fistula and even washed 
out. Thus, recently eaten and little contami- 
nated forage samples are collected for analy- 
ses. Since emptying the rumen prior to collect- 
ing forage samples disrupts normal digestive 
processes, animals for qualitative forage sam- 
pling are not usually used in concurrent range 
digestibility trials. 
Esophageal fistulation for nutritional studies 
has been reviewed by Van Dyne and Torell 
(1964), who described the technique in detail. 
Such surgically modified animals apparently 
feed like normal animals, and the forages col- 
lected before reaching the stomach can be used 
to determine both food habits and nutrient 
composition. Sampling range vegetation by 
esophageal fistulation is easier and provides a 
better measure of between-animal variations 
than does sampling from ruminally fistulated 
animals (Bohman and Lesperance 1967). 
The usual procedures for measuring forage 
utilization (Forest Service, U.S. Dep. Agr., 
1963) provide estimates that are too imprecise 
for defining either forage components ingested 
or daily food consumption. 
Quantitative Estimates of Range Forage 
Intake 
Forage intake may be estimated from fecal 
collection data obtained in conjunction with 
range digestion trials. On homogeneous ranges, 
excreta is collected from bags attached to graz- 
ing animals. Dry-matter (DM) digestion of 
clipped range plants is determined from stan- 
dard digestion trials conducted under dry-lot 
conditions. Feed intake is calculated from 
weight of bagged fecal material, with the DM 
eaten: DM excreted ratio obtained in digestion 
trials. Other forage partitions besides DM 
ee been similarly used to estimate feed in- 
take. 
82 
Indigestible indicators contained in the for- 
ages and concentrated in the feces are also 
used to estimate food consumption. In this 
technique, total indicator concentration in a 
day’s fecal matter is divided by the food indi- 
cator concentration: (2) 
Dry matter consumption (g./day) = 
Units indicator/ g. dry matter 
g. dry feces in daily feces 
Units indicator/g. forage dry matter 
The merits of several indicators, including lig- 
nin, plant chromogens, and silica, are described 
by Van Dyne and Meyer (1964a). 
On heterogeneous range, two sets of animals 
are usually used. The first, esophageally or 
ruminally fistulated, yields food samples for 
analysis of internal plant indicators. The sec- 
ond group of animals are equipped with har- 
nesses and collection bags to obtain fecal mate- 
rials (Van Dyne and Meyer 1964b; Bohman 
and Lesperance 1967). With wild animals this 
technique would incorporate the obvious diffi- 
culties of maintaining and capturing both 
groups of animals. 
Van Dyne and Meyer (1964b) recently de- 
scribed measurement of forage intake in bifis- 
tulated animals. Forage samples collected 
through esophageal fistulas can be used for de- 
termining food habits as well as for nutrient 
and indicator analyses. Total excreta is ob- 
tained daily from fecal collection bags. The di- 
gestibility of forage cellulose is determined 
from 48-hour in vitro microdigestion with 
rumen liquor obtained through a rumen fistula. 
This information is also measured by inserting 
forage samples in nylon bags into the rumen 
through the fistula. Total forage intake per 
day can then be calculated from the total cellu- 
lose excreted per day and the cellulose content 
of forage samples. Forage cellulose levels are 
corrected for percent of cellulose digested and 
not represented in the fecal samples. The ad- 
vantage of the procedure is that, for cows and 
sheep, estimates of food ingestion and digest- 
ibility can be obtained from one grazing ani- 
mal. Procedures requiring bifistulated animals 
probably have little potential for wild herbi- 
vores. 
Determining Apparent Digestibility of 
Range Forage 
On very homogeneous pastures, freshly 
clipped forages can be utilized in standard 
dry-lot digestion trials. On very heterogeneous 
ranges, the value of this procedure is doubtful, 
since plants subjectively clipped and freshly 
fed may not adequately reflect the diet chosen 
by the animal. 
On heterogenous ranges, forage digestibil- 
lity is measured with naturally occurring and 
indigestible forage indicators. Apparent digest- 
