equal to the reciprocal of indicator recovery 
most of the studies cited (table 6) would over- 
estimate fecal excretion and thus forage in- 
take. Chromic oxide recovery in total fecal col- 
lections ranged from 90 to 102 percent for 
paper administration. Estimated recovery from 
grab samples varied from 72 to 113 percent. 
The lack of information on the use of chromic 
oxide paper and grab sampling techniques with 
livestock grazing native range is apparent. 
Fewer studies have been reported on the use 
of chromic oxide-cellulose mixtures (table 6); 
however, animal numbers approach those in 
studies with chromic acid paper. Most of the 
cellulose mixture trials were conducted under 
range conditions, with single or twice-daily 
grab sampling. Recovery values ranged from 
76 to 101 percent for total collection samples 
and from 80 to 104 percent for grab samples. 
The low recovery values noted in these stud- 
ies are difficult to explain. Incomplete recov- 
eries with chromic oxide powder have been 
noted by several workers (Crampton and 
Lloyd 1951; Clanton 1962; Johnson et al. 
1964). Retention or absorption of chromic 
oxide powder in the digestive tract appears to 
be of minor importance (Carter et al. 1960). 
Small fecal losses in the total collection meth- 
ods are to be expected and probably account 
for some apparently low recoveries. The mag- 
nitude of this error with the use of collection 
bags in studies with animals grazing range 
forage is difficult to determine. Partial recov- 
ery of the chromic oxide in the fecal material 
does not limit the usefulness of the indicator 
for estimating fecal output, since appropriate 
adjustments can be made if the percent recov- 
ery is constant. 
Regurgitation of gelatin capsules containing 
chromic oxide paper or cellulose mixtures has 
been noted by several workers (Corbett et al. 
1960; Streeter 1966;7 McCann 1967)*. The 
“sustained release pellet,” which is composed 
of chromic oxide and plaster of Paris (Pigden 
and Brisson 1957), has not been satisfactory 
with sheep due to regurgitation (Corbett et al. 
1960). Streeter (1966) * placed capsules con- 
taining chromic oxide paper directly into the 
esophageal fistula of steers to alleviate this 
problem. Green et al. (1966) did not note re- 
gurgitation of shredded paper containing 
chromic oxide that was wrapped in paper and 
was given orally without capsules. Howard 
(1965) ® placed chromic oxide cellulose mix- 
_' Streeter, C. L. 1966. Methods of estimating the 
digestibility and voluntary intake of range forage 
consumed by grazing cattle. Unpublished Ph.D. Disser- 
tation on file at University of Nebraska, Lincoln, 
Nebr. 
* See footnote 5, page 114. 
* Howard, M. L. 1965. Unpublished data on file at 
University of Arizona, Tucson, Ariz. 
tures (wrapped in filter paper) directly into 
the rumen of fistulated steers. 
Fecal excretion of chromic oxide apparently 
is altered by feeding condition (hand fed vs. 
grazing) as well as by time of fecal grab sam- 
pling and indicator administration (table 6). 
Langlands et al. (1963), using chromic oxide 
paper once daily, obtained recoveries of 106, 
72, and 90 percent with grazing sheep as mea- 
sured by morning, evening, and combined 
morning and evening grab samples. The mean 
standard deviation of the difference between 
fecal collection and estimated fecal output 
from the morning grab samples was +24 per- 
cent, as compared to the corresponding value 
of +13 percent obtained from both morning 
and evening samples. 
Arizona workers (McCann and Theurer 
1967) found grab sampling once daily (7:30 
a.m.) at the time of administration of a 
chromic oxide-cellulose mixture satisfactorily 
estimated fecal output from steers fed alfalfa 
hay under controlled conditions (table 7). 
Under range conditions, this same _ tech- 
nique overestimated fecal excretion by 24 
percent (Galt et al. 1968).'° The studies of 
Green et al. (1966) showed that fecal output of 
cattle would be underestimated by 12 percent 
using every-other-day grab sampling with con- 
comitant administration of chromic oxide 
paper. Their studies were conducted under con- 
fined conditions and may not be applicable 
under range conditions. 
Corbett et al. (1966), using shredded 
chromic oxide paper, suggested that 14 grab 
samples from sheep (twice daily per animal), 
would estimate chromic oxide concentration 
within a standard error of +3 percent. McCann 
(1967) 1! administered a chromic oxide-cellu- 
* Galt, H. D., Theurer B., and Martin, S. C. 1968. 
Unpublished data. University of Arizona and Rocky 
Mountain Forest and Range Experiment Station, Tuc- 
son, Arizona. 
™ See footnote 5, page 114. 
TABLE 7—E'stimated fecal output from chromic 
oxide concentration in single daily fecal grab 
samples }? 
Estimated output 
Trial Forage Steers Actual Output Percent 
output * of 
actual 
output 
Number Gm./ Gm./ 
ay day’ 
1 Hay, hand fed 8 2,148 2,413 111.4 
2 TD) Ogee eee tenes 8 3,168 3,196 99.7 
3 Native range - 4 2,926 3,634 124.2 
1McCann and Theurer (1967). See footnote 11, above 
(Galt et al. 1968). . 
? Chromic oxide mixed in a 1:2 ratio with cellulose 
and administered once daily. 
* Dry matter basis. 
117 
