lose mixture to cattle once daily and calculated 
that four animals and 12 days were required, 
with single daily grab samples, to obtain a 95 
percent confidence interval of +10 units of the 
recovery mean with a probability of 95 per- 
cent. Van Dyne and Meyer (1964) determined 
that the average number of animals required 
to estimate forage intake from a dry annual 
range using lignin ratio and total fecal collec- 
tion methods would be 4 and 22 sheep or 2 and 
6 cattle to sample forage and feces, respec- 
tively. 
SUMMARY 
Use of chemical indicators to measure forage 
consumption indirectly, by estimating digest- 
ibility and fecal excretion, presents unique 
problems under range conditions. Lignin has 
been the primary internal indicator used to es- 
timate digestibility of range forages, and 
chromic oxide is the most common external in- 
dicator for measurement of fecal output. 
Hand sampling of forage representative of 
that ingested by a grazing animal is not possi- 
ble because of pronounced grazing selectivity 
from the heterogeneous, seasonally changing 
plant composition available on native range- 
land. The use of esophageal- or rumen-fistu- 
lated animals is the best method for sam- 
pling the grazing animal’s diet. Fistulation per 
se does not appear to affect forage digestibility. 
However, evacuation of rumen-fistulated cattle 
to obtain forage samples during the digestion 
study may lower digestibility values. It should 
also be recognized that if rumen-fistulated ani- 
mals are used to measure fecal output, forage- 
consumption values will be biased downward 
compared to nonfistulated animals of similar 
age and weight. 
Preparation of fistula forage samples for 
chemical analyses is a critical step because the 
method of drying appears to alter certain frac- 
tions, notably lignin. The increased concentra- 
tion of lignin in rumen fistula forage samples 
relative to conventional forage samples 
markedly limits the usefulness of the lignin 
ratio technique until causative factors can be 
quantified and refinements can be made to cor- 
rect the inflated lignin values. Acid detergent 
lignin has an apparent digestibility in alfalfa 
hay of approximately 10 percent. The recovery 
of acid detergent lignin from other plant spe- 
cies is not known and needs to be determined to 
permit measurement of the digestibility of 
range forage. 
Erratic recovery of chromic oxide in fecal 
grab samples and loss of the indicator by re- 
gurgitation of gelatin capsules have been the 
major problems limiting the use of chromic 
oxide under grazing conditions. Incomplete re- 
covery of the indicator does not invalidate the 
technique if percent recovery is constant and 
can be reasonably quantified. The introduction 
of chromic oxide in shredded paper and 
chromic oxide-cellulose mixtures has markedly 
reduced variation in fecal excretion of the indi- 
eator under grazing conditions. Administration 
of chromic oxide paper in paper boluses may 
minimize losses due to regurgitation. 
Although refinement of the indicator meth- 
ods is needed, recent research has clarified the 
variables so that meaningful forage consump- 
tion values appear possible with these tech- 
niques. 
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