that the difference could have been attributed 
to decreased consumption by the harnessed 
steers. 
Because of the difficulties associated with 
total fecal collection coupled with the brushy 
nature of many native ranges, many investiga- 
tors have utilized an external indicator to esti- 
mate fecal output. Fecal excretion is deter- 
mined from the relationship of indicator ad- 
ministered to that excreted: 
Fecal dry matter output (gm) = 
gm. Indicator administered 
gm. Indicator/gm. fecal dry matter 
The disadvantage of this method is that the 
animals must be assembled one or more times 
daily so the indicator can be administered and 
fecal grab samples can be collected. Accurate es- 
timation of fecal output by use of an external 
indicator depends upon a constant or a 100-per- 
cent recovery of the material in the feces. 
Chromic oxide (Cr.0;) has been the most fre- 
quently used external indicator. 
Chromic Oxide Recovery as Influenced by 
Method of Administration 
Chromic oxide has been administered in var- 
ious forms and at different intervals to reduce 
variability in fecal excretion of the indicator. 
Considerable diurnal variation has been re- 
ported with the use of chromic oxide powder, 
whether mixed with the ration (Kane et al. 
1952) or administered in gelatin capsules 
(Hardison and Reid 1953; Pigden and Brisson 
1957; Raymond and Minson 1955). Irregulari- 
ties in feeding pattern and animal behavior 
enhance irregularities in excretion by cattle 
and sheep (Balch et al. 1957). Fecal concentra- 
tion of chromic oxide has been shown to be 
more variable in grazing than in hand-fed ani- 
mals (Hardison and Reid 1953; Raymond and 
Minson 1955). 
Administration of chromic oxide powder in 
gelatin capsules and collection of fecal grab 
samples at the same time twice daily has been 
successfully employed with cattle grazing for- 
age (Lesperance and Bohman 1963; Connor et 
al. 1963). These workers found that fecal ex- 
cretion values were essentially the same 
whether determined by grab samples or total 
collection. Other workers have noted consider- 
able variability in the use of chromic oxide 
powder under range conditions (Bohman et al. 
1967). 
Corbett et al. (1958) reported that incorpo- 
ration of chromic oxide in paper gave more 
uniform flow of the indicator through the duo- 
denum of sheep than administration of 
chromic oxide powder in gelatin capsules. 
Later studies (Corbett et al. 1960) indicated 
that administration of chromic oxide in shred- 
ded paper significantly reduced the variability 
of fecal excretion in sheep as compared to the 
powdered form given in an oil suspension. In 
Similar comparisons with both cattle and 
sheep, Cowlishaw and Alder (1963) and Lang- 
lands et al. (1963) reported less variation in 
fecal concentration with the shredded-paper 
technique. 
Bohman et al. (1967) reported on studies 
conducted at the Oregon station in which the 
variation in fecal chromic oxide recovery was 
reduced by mixing the indicator with cellulose. 
In three trials conducted with steers grazing 
native range, recovery from total collection 
samples averaged about 100 percent, with a 
range of from 88 to 112 percent, when the cel- 
lulose mix was administered twice daily in gel- 
atin capsules. When fecal grab samples were 
taken twice daily at the time of dosing, the es- 
timated fecal output averaged about 99 percent 
of actual dry-matter excretion. 
Chromic oxide administration and collection 
of grab samples at less frequent intervals 
would be extremely advantageous under most 
range conditions. McCann (1967) ® found that 
administration of a chromic oxide-cellulose 
mixture once daily resulted in rather constant 
excretion of chromic oxide from the fourth to 
twelfth day of administration from steers 
hand-fed alfalfa hay (table 5). Daily recovery, 
expressed as a percent of the mean for each 9- 
day study, ranged from 94 to 110 percent and 
from 94 to 108 percent in trials 1 and 2, respec- 
tively. Day-to-day variations in fecal excretion 
were not significant. These studies agree with 
similar data reported by Green et al. (1966) 
for chromic oxide paper administered once 
daily. 
Use of Chromic Oxide in Paper or Cellulose 
Mixtures.—Various studies in which chromic 
oxide paper or chromic oxide-cellulose mix- 
tures have been given to cattle or sheep are 
* See footnote 5 p. 114. 
TABLE 5.—Daily recovery of chromic owide ex- 
pressed as percent of mean recovery.» * 
Day * Trial 1* Trial 2* Average 
4 102.1 106.9 104.5 
5 99.8 98.1 98.9 
6 96.6 107.7 102.2 
7 95.7 103.8 99.8 
8 98.9 96.6 97.8 
9 100.7 98.6 99.6 
10 94.4 94.0 94.2 
11 110.0 95.7 102.8 
12's 101.6 98.3 100.0 
* See footnote 5, p. 114. 
* Chromic oxide mixed in a 1:2 ratio with cellulose 
and administered once daily in gelatin capsules. 
* Days after initial administration of indicator. 
* Average of eight steers per trial. 
115 
