In work in Wyoming,® esophageal samples 
of forage dried at 60° C. were significantly 
lower in ash than samples frozen after collec- 
tion. The nitrogen, cellulose, and acid-deter- 
gent lignin contents were not significantly af- 
fected by sample preparation: 
Frozen Dried 
Percent’ Percent 
PASI ets eres ae ee oe ca one 19.3 12.3 
Nitrogen * (32. 2 22ee oh See eee 2.9 2.8 
Cellulose?: 22/22 ase peer 32.2 29.9 
Acid detergent lignin? ___________ 2.3 2.4 
*Means with different superscripts are significantly 
different (P<.01). 
* Dry matter basis. 
Also, dry matter was significantly reduced 
and ash was significantly increased when sam- 
ples of alfalfa were collected through esopha- 
geal fistulae in steers; acid-detergent lignin 
tended to be higher. Rinsing the esophageal 
samples with tapwater further reduced the dry 
matter. Rinsed samples had _= significantly 
higher cellulose, lower ash, and lower nitrogen 
than esophageal samples analyzed without rins- 
ing. The rinsing of esophageal samples had a 
large effect on the chemical constituents of 
samples: 
After 
Before collection * 
collection’ Notrinsed Rinsed 
Percent Percent Percent 
Dry matter _________. 52.3 ° 14.6? 11.4° 
Ashe 2) 2 oi el ee 8.4* 16.8” 7.8 ° 
Nitrogen? ___________ 3.24 * 3.02 2:5; 
Cellulose? ___________ 30.2 * 28.0? 31.8” 
Acid detergent lignin?. 1.49? 2.2F8 2.5% 
Means with different superscripts are significantly 
different (P<.01). 
* Dry matter basis. 
DETERMINATION OF DIET DIGESTIBILITY 
Once a representative sample of the diet has 
been collected, the digestibility may be deter- 
mined by the use of the artificial rumen 
(Barnes 1965; Johnson 1966; Van Dyne 1962). 
The in vitro artificial rumen techniques cur- 
rently in use may be classified generally into 
two types: (1) microbial digestion of dry mat- 
ter or cellulose and (2) a two-stage system 
where preliminary microbial digestion is fol- 
lowed by an acid-pepsin treatment to remove 
the effects of microbial or forage protein (Til- 
*Cundy, D. R., and Rice, R. W. 1968. Salivary con- 
tamination by esophageal collection with steers. (Un- 
published data). Univ. Wyo., Laramie, Wyo. 
ley and Terry 1963). The in vitro or artificial 
rumen is very useful for predicting the in vivo 
digestibility of forages and complements the 
collection of diet samples by fistulated animals. 
The rate of fermentation in vitro is apparently 
related to the voluntary intake of forages (Do- 
nefer et al. 1960). Digestibility data coupled 
with estimates of fecal excretion can give reli- 
able estimates of intake of forages. If the bo- 
tanical composition of the diet is known, the 
intake of individual species of forage may be 
estimated. Similarly, when the chemical com- 
position of the diet is known, nutrient balances 
may be determined. 
SUMMARY 
The diet of grazing ruminants can be sam- 
pled by using fistulated animals. In this way 
the animal itself expresses its preference for 
plant species or portions of plants. The use of 
esophageal fistulas is preferable to the use of 
rumen fistulas because rumen evacuation (1) 
subjects the experimental animals to unphys- 
iologic conditions, (2) is limited to large ani- 
mals, and (3) is more laborious. Although 
complete botanical identification of fistula sam- 
ples is possible, the variation within animals in 
their selection of plant species limits the accu- 
rate estimation of the contribution of plants 
making up a minor portion of the diet. The bo- 
tanical analysis of fistula samples will yield 
quantitative information about animal prefer- 
ences for the major species of the diet. 
Chemical analyses of fistula samples are 
complicated by salivary additions during col- 
lection. Saliva adds moisture and minerals, and 
may or may not add nitrogen to the collected 
sample. The composition and amount of saliva 
added to fistula samples varies with the nature 
of the diet. Collected samples must be handled 
carefully because rinsing, drying, drainage 
of excess saliva, and other procedures prepara- 
tory to analysis will affect chemical constitu- 
ents. The fibrous analysis appears to be af- 
fected least, whereas the effects of collection 
and handling on nitrogen, phosphorus, and sol- 
uble carbohydrate analyses may be consider- 
able. 
Fistula collection is the best method now 
available for obtaining quantitative informa- 
tion about the botanical and chemical nature of 
the diet of grazing animals. 
LITERATURE CITED 
Arnold, G. W., McManus, W. R., Bush, I. G., and Ball, J. 
1964. The use of sheep fitted with oesophageal fistu- 
las to measure diet quality. Aust. J. Exp. 
Agr. and Anim. Husb. 4: 71. 
Bailey, C. B., and Balch, C. C. 
1961. Saliva secretion and its relation to feeding in 
130 
cattle: II. The composition and rate of se- 
cretion of mixed saliva in the cow during 
rest. Brit. J. Nutr. 15: 383. 
Barnes, R. F. 
1965. Use of in vitro rumen fermentation techniques 
for estimating forage digestibility and in- 
take. Agron. J. 57: 213. 
