Stomach Content Analyses: A Comparison of the Rumen vs. Esophageal Techniques * 
RICHARD W. RICE? 
Grazing animals have the opportunity to de- 
termine their dietary intake through selective 
grazing. Where a choice exists, they may pre- 
fer certain species of plants. They are also ca- 
pable of selecting more palatable portions of 
plants. The capability of animals to eat selec- 
tively has been emphasized by Bredon and 
Marshall (1962), who found that cattle con- 
sumed a nutritionally superior hay than that 
offered. Animals have much greater opportu- 
nity for selection while grazing mixed vegeta- 
tion. Therefore, it has been difficult to define 
the botanical and chemical composition of diets 
of grazing animals. 
The diets of grazing animals have been stud- 
ied by visual observation of the plants grazed 
(Halls 1954; Smith et al. 1959; Reppert 1960), 
stomach content analyses (Martin and Korsch- 
gen 1963), analyses of fecal material for frag- 
ments of plants eaten (Croker 1959; Stewart 
1967), simulation of diet by hand plucking 
(Edlefsen et al. 1960; Cook 1964), and clip- 
ping and analyzing pastures before and after 
grazing (Peterson et al. 1956; Carter et al. 
1960). 
These methods have not been entirely satis- 
factory for determining the exact chemical and 
botanical composition of the grazing animals’ 
diet. Ruminant animals are particularly diffi- 
cult to work with, since the mixing, rechewing, 
and selective passage of dietary materials 
through the digestive tract may confuse or bias 
analyses of stomach contents or of fecal mate- 
rial. The rumen contents of grazing animals 
contain the residues of certain forages eaten as 
much as 10 days before sampling, whereas cer- 
tain other components of the diet may remain 
in the rumen for only short periods. Thus, 
stomach and fecal analyses may be seriously 
biased toward more fibrous or less digestible 
materials in the diet. Norris (1943) found 
large variability between the botanical analy- 
sis of the forage fed and the botanical analysis 
of the rumen ingesta of sheep. 
The success of the quantitative determina- 
tion of animal food habits depends on an exact 
knowledge of the botanical and chemical con- 
tent of the diet. Fistulation techniques seem to 
be the methods chosen. The purpose of this ar- 
1Approved as Scientific Report SR 120 by the 
Director, Wyoming Agricultural Experiment Station, 
Laramie, Wyo. 
? Associate Professor of Animal Husbandry, Divi- 
sion of Animal Science, University of Wyoming, Lara- 
mie, Wyo. 
ticle is to discuss ruminal-and esophageal-fis- 
tulae techniques for obtaining samples of a 
grazing animal’s diet. 
DEVELOPMENT AND USE OF 
ESOPHAGEAL FISTULAE 
The technique of esophageal fistulation is 
not new. It was reported in 1855 by Claude 
Bernard; Pavlov conducted studies with dogs 
in 1889 (cited by Van Dyne and Torell 1964). 
The use of this technique has been hindered by 
difficulties associated with esophageal anatomy 
(McManus 1961). The esophagus does not have 
an enclosing serosa; it has a poor blood sup- 
ply; the fistulation restricts the necessary 
movement of the esophagus; and scar tissue 
that further restricts the function of the mus- 
culature often forms. Food blockage often oc- 
curs, and animals will die if it is not removed. 
In some cases the muscular tone and action of 
the esophagus is impaired, and the animals 
cannot swallow ingested food. The cannula 
may be expelled; extensive salivary loss and 
serious dehydration may occur within a few 
hours. 
Various surgical techniques have been de- 
scribed ;? the procedures used at the Wyoming 
Station were similar to those of Van Dyne and 
Torell (1964). 
Closures for the fistula have generally been 
of two types, a permanent cannula (Cook et al. 
1958; Rusoff and Foote 1961) or a removable 
plug (Van Dyne and Torell 1964; McManus 
1962). The removable plug has been used at 
the Wyoming Station, since a larger opening is 
maintained and a more complete collection of 
ingested food is possible. The size of a fistula is 
important. Blackstone et al. (1965) obtained a 
more complete collection of ingesta from sheep 
with a larger opening. 
In early developmental stages of esophageal 
surgery, animal losses were great. For in- 
stance, McManus (1962) established fistulae in 
35 sheep and found that only 5 were suitable 
for field studies, and Torell (1954) had success 
with only 1 of 4 sheep. Cook et al. (1958) were 
able to use three of four sheep; however, they 
lost all of a second group of four fistulated 
sheep for various reasons. Cook et al. (1961, 
1962) have used fistulated sheep successfully 
under range conditions. Lesperance et al. 
(1960) were unsuccessful with 4 esophageal- 
>Torell 1954; Cook et al. 1958; Hamiliton et al. 
1960; McManus 1962; Chapman and Hamilton 1962; 
Cook et al. 1963; Van Dyne and Torell 1964. 
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