The Use of the Esophageal Fistula for the
Determination of Consumption and
Digestibility of Pasture Forage by Sheep
Donald L. Bath, William C. Weir and Donald T.
Torell
J ANIM SCI 1956, 15:1166-1171.
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T H E USE OF T H E ESOPHAGEAL FISTULA FOR T H E DET E R M I N A T I O N OF CONSUMPTION AND
D I G E S T I B I L I T Y OF PASTURE
FORAGE BY SHEEP 1, 2
DONALD L.
BATH, 3 WILLIAM
C.
W E I R 4 AND D O N A L D T .
TORELL 5
University o] California, Davis
M E T H O D of obtaining representative samples of forage a c t u a l l y
eaten by grazing animals has long been a problem. The many
methods previously proposed are time consuming and tedious. The use
of the esophageal fistula in grazing animals offers a new approach to
this problem (TorelI, 1954). This paper reports results obtained in
testing this technique with these fistulated sheep.
Once a representative sample of forage is obtained, several techniques
are available for the determination of consumption and digestibility.
Reid et al. (1950) have proposed the use of chromogens in the feces.
Cook and Harris (1951) had difficulty in using this technique under
range conditions. The lignin ratio method proposed by Forbes and
Garrigus (1948) appears to be more applicable to all types of forage.
Variation in the reported digestibility of lignin introduces some doubt
in the accuracy obtained but most results indicate that lignin is only 0
to 5% digestible. Chromic oxide as an indicator substance has been used
successfully in mixed rations but its effective use on pasture is limited
because of the difficulty encountered in getting it uniformly mixed with
the ingested forage.
E x p e r i m e n t a l and Results
Effect o] Collection on the Sample
A study was conducted to test this technique on any change which
might take place in forage while in the mouth before dropping out of
the fistula. Chopped alfalfa hay was thoroughly mixed and divided into
four lots by the quartering method. One lot was taken for chemical
x This research was supported in part by Western Regional Project W-34.
The authors wish to express their appreciation to G. P. Lofgreen and J. H. Meyer for their
advice in connection with this research.
s Present address: Santa Rosa High School, Santa Rosa, California.
Associate Professor of Animal Husbandry, Davis.
Associate Specialist in Animal Husbandry, Hopland Field Station.
1166
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ESOPHAGEAL FISTULA FOR PASTURE STUDIES
1167
analyses and the other three lots were fed to a fistulated wether. The
three samples collected from the fistulated wether were weighed and
analyzed for comparison with the control sample. Results are shown in
table 1.
Examination of the analyses indicate that there was little change in
the chemical composition of the material during the collection procedure.
The ash content of the collected material appears to be somewhat higher
than for the control sample. It is theoretically possible to explain this
TABLE 1. COMPARISON OF COMPOSITION OF ALFALFA HAY BEFORE
AND AFTER PASSING THROUGH T H E MOUTH AND AN
ESOPHAGEAL FISTULA
Dry matter composition
Dry
matter
fed
gm.
Wet
Dry
collec- matter
tion collected
gm.
gm.
Control
Fistula
Collection I
Collection I I
Collection I I I
151.7
167.3
145.2
573
804
578
148
165
148
Ash
Ether
Protein extract
Crude
fiber
Nitrogen
free
extract Lignln
%
%
%
%
%
%
12.0
27.8
1.3
22.4
36.5
6.8
12.3
12.9
12.8
27.4
27.5
27.4
1.3
1.2
1.2
22.2
22.2
22.5
36.8
36.2
36.1
6.4
6.4
6.3
on the basis of the mineral content of the saliva. The saliva excretion was
estimated by the increase in weight of the material as fed and as collected. This increase is shown in table 1. If the saliva is assumed to
contain 0.5% mineral, this amount of mineral would increase the ash
content of Collection I by 1.4%, Collection II by 1.9%, and Collection
III by 1.4%. The ash results would indicate that the effect is somewhat
less than estimated by this method. The slightly lower lignin content
of the collections compared to the control sample, while within the experimental error of the analyses, m a y also reflect some selection of the
portion of the sample eaten by the wether as there was a small weighback in every case. This would not be a factor in pasture collections as
only the part actually eaten is of interest. McDougall (1948) reported
sheep saliva contained 0.7 to 0.9% ash.
Consumption and Digestion Trials
With the above test indicating that there was little change in forage
during the esophageal fistula collection, trials were conducted on three
types of irrigated pastures. Two esophageal fistulated ~wethers were used
to make collections of the pasture forage. Since Collections and leakage
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1168
BATH, WEIR AND TORELL
at the fistula decrease the a m o u n t of feed actually taken into the digestive tract b y the fistulated animals, it was thought desirable to take
fecal collections from three normal non-fistulated wethers which had been
fitted with fecal collection bags. This technique was therefore based on
the assumption that all five sheep ate the same quality of forage from
the pastures. T h e three wethers used for fecal collections weighed 84,
89, and 12 7 lb. at the conclusion of the trials.
TABLE 2. CHEMICAL COMPOSITION ON ESOPHAGEAL FISTULA
COLLECTIONS AND HAND CLIPPED FORAGE FROM
THREE KINDS OF PASTURE
% Dry basis
Pasture
Sheepno.
Sudan
Sudan
Sudan
Sudan
Sudan
Sudan
1
3
1
3
1
3
Sudan
Sudan
Trefoil
Trefoil
Trefoil
Trefoil
Trefoil
Alfalfa
Alfalfa
Alfalfa
Alfalfa
Alfalfa
Date
August 12
August 12
August 14
August 14
August 17
August 17
Average6 collections
Hand clipped August 17
3
3
3
3
August 27
August 29
August 30
August 30
Average 4 collections
1
3
1
September 13
September 13
September 16
Average 3 collections
Hand clipped September 18
Ash
Protein
Lignin
Ether
extract
14.6
13.4
14.0
12.0
16.6
11.6
15.5
16.1
14.5
13.6
16.8
14.7
8.4
8.4
8.8
9.3
9.7
8.5
1.59
1.62
1.75
1.52
I. 74
1.30
13.7•
12.2
15.2•
8.1
8.85•
6.5
1.59•
1.61
13.0
11.9
11.9
11.2
25.8
28.2
26.8
27.2
6.9
7.1
5.9
6.4
2.60
2.88
2.37
2.47
12.0•
27.0•
6.6•
2.58•
10.8
14.8
10.5
27.3
24.5
22.2
6.6
5.6
7.4
1.63
1.89
1.86
12.0-----2.424.7~---2.9 6.5~---.9 1.79•
8.8
21.6
5.5
2.13
T h e five wethers were placed in each pasture one week before the
actual trials were conducted in order that they might become accustomed
to the forage a n d to allow time for previous feed' to clear the digestive
tract of the wethers used for fecal collections.
Fistula collections were attempted at the beginning, mid point, and
near the end of each test period. Some difficulty was encountered in some
of the collections so results are reported only where forage samples adequate for analyses and free of r u m e n contents were obtained. (An occasional collection was ruined b y regurgitation.)
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ESOPHAGEAL FISTULA FOR PASTURE STUDIES
1169
For comparative purposes, square-foot plots randomly located in the
sudan and alfalfa pastures were hand clipped. The analyses of the
esophageal fistula collections and the hand-clipped samples are shown
in table 2.
The sudan pasture tested was almost pure Sudan grass. The pasture
had been previously grazed and clipped. Most of the plants were about
six to eight inches high and in the vegetative stage during the test. A
small amount of Sudan on the irrigation checks and near the fence was
more mature with seed heads developing.
The trefoil was a 91~o pure stand of narrowleaf birdsfoot trefoil
(Lotus tenuis) with yellow star thistles and peaweed as impurities.
When grazed it was about eight inches high with some blooms and some
seed heads developing.
The alfalfa field was a pure stand of alfalfa with a small amount of
dry weedy material around the fences. The stage of maturity was somewhat variable due to some dry, sandy areas in the pasture, and varied
from no bloom in some areas to 100~o bloom in others.
The feces were collected from the three intact wethers twice daily,
dried, weighed, and an aliquot taken for analyses for ash, lignin, and
nitrogen. Using the lignin-rafio method of Forbes and Garrigus (1948)
and the total digestible nutrients method of Lofgreen (1953), daily dry
matter consumption, total digestible nutrients and percent digestible
protein were calculated. (table 3).
Discussion
The use of fistulated wethers to collect representative samples of
pasture or range forage and similar intact wethers to collect feces from
such forage gives promise of a useful technique for measuring consumption and digestibility of such forage. Further refinements of the technique are needed for more precise results. The forage collections should
precede the fecal collections by an interval equal to the time it takes
the forage under study to pass through the digestive tract. This could be
obtained by giving a marker to the intact sheep when turned into a
study area.
More data are needed to determine the variability between samples
collected by the same fistulated sheep on the same pasture. Data are also
needed on the variability of samples collected by different fistulated
sheep on the same pasture. Studies currently underway on this subject
will be published in a later paper.
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1170
B A T H , W E I R AND TORELL
T A B L E 3. R E S U L T S C A L C U L A T E D F R O M F E C A L C O L L E C T I O N S
Daily
Daily
fecal wt.
feed intake
dry matter dry matter
Pasture
Sheep
no.
gm.
gm.
%
%
%
Sudan
Sudan
Sudan
13
32
65
412
366
345
828.7
653.4
643.2
48.0
45.3
46.7
56.8
44.5
44.7
8.6
6.8
6.8
Trefoil
Trefoil
Trefoil
13
32
65
381
309
350
1166.1
997.3
1145.5
63.4
64.7
64.9
78.7
76.3
78.1
21.2
20.6
21.1
Alfalfa
Alfalfa
Alfalfa
13
32
439
411
339
1350.8
1138,2
964.8
62.4
59.7
59.8
76.5
71.7
75.2
18.9
17.7
18.6
65
T.D.N
dry-basis
Protein
Digestible
digestibility protein
The most difficult task in connection with this procedure was keeping
the fistulated sheep in good health and in condition to make the collections. Experience t o date indicates that the fistulated sheep require
careful daily attention. The fistula may be kept closed with double
layers of plastic--one layer in the esophagus and a second on the outside
of the skin---and the two laced together with heavy nylon fishline. Two
of the wethers used for these studies (No. 1 and 3) were operated on in
~[une, 1954, and were in thrifty condition 20 months later.
Collection periods should not exceed 30 minutes or the sample may be
lost by regurgitation and contamination with rumen contents. Larger
collections can usually be obtained by keeping the fistulated wethers off
feed the night preceding the collection period.
T A B L E 4. C O M P A R I S O N OF T E S T R E S U L T S W I T H M O R R I S O N ' S R E QUIREMENTS FOR "GROWING EWE LAMBS AND YEARLINGS"
IN THREE WEIGHT CLASSIFICATIONS
80-lb. lambs
90-lb. lambs
120-lb. lambs
lb.
lb.
lb.
Dry matter
Required a
Sudan test
Trefoil test
Alfalfa test
2.2-2.7
1.4
2,5
2.1
2.3-2.8
1.4
2.2
2.5
2.6-3.
1.8
2.6
3.0
Total digestible nutrients
Required a
Sudan test
Trefoil test
Alfalfa test
1.4-1.7
.7
1.6
1.3
1.5-1.8
.6
1.4
1.5
1.8-2.
.9
1.6
1.9
a Morrison's table III.
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ESOPHAGEAL FISTULA FOR PASTURE STUDIES
1171
A comparison of the results obtained from this test with Morrison's
(1948) requirements for l a m b s is shown in table 4. T h e low intake on
the Sudan p a s t u r e m a y in p a r t be due to the fact t h a t the intact lambs
were not accustomed to the fecal collection bags. T h e values obtained
on the trefoil and the alfalfa compare rather favorably with Morrison's
tables. F u r t h e r trims are needed to determine the gain of lambs on
pasture and determine the actual intake of d r y m a t t e r and T . D . N . of
such lambs on the pasture.
Summary
A test conducted to s t u d y the change in chemical compositio~ of
forage during the process of passing through the mouth and out an
esophageal fistula indicated that there was little difference between the
sample fed and t h a t collected from the fistula.
A technique is described in which esophageal fistulated wethers were
used to collect samples of Sudan grass, trefoil, and alfalfa pasture as
consmned b y grazing sheep and normal wethers equipped with f e c a l
collection harnesses were used to collect feces. Assuming that all sheep
are eating the same quality forage and using the lignin-ratio procedure,
d r y m a t t e r consumption, total digestible nutrients, and digestible protein of the pasture forage were calculated.
I m p r o v e m e n t s and possible use of this technique are discussed.
Literature
Cited
Cook, C. Wayne and Lorin E. Harris. 1951. A comparison of the lignin ratio
technique and the chromogen method of determining digestibility and forage
consumption of desert range plants by sheep. J. Animal Sci. 10:565.
Forbes, R. M. and W. P. Garrigus. 1948. Application of a lignin ratio technique to
the determination of the nutrient intake of grazing animals. J. Animal Sci.
7:373.
Lofgreen, G. P. 1953. The estimation of total digestible nutrients from digestible
organic matter. J. Animal Sci. 12:359.
McDougall, E. I. 1948. Studies on ruminant saliva I. The composition and output
of sheep's saliva. Biochem. J. 43:99.
Morrison, F. B. 1948. Feeds and Feeding. The Morrison Publishing Company,
Ithaca, New York.
Reid, J. T., P. G. Woolfold, C. R. Richards, R. W. Kaufmann, J. K. Loosli, K. L.
Turk, J. I. Miller and R. E. Blaser. 1950. A new indicator method for determination of digestibility and consumption of forages by ruminants. J. Dairy
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