- A Cr₂0₃, and cellulose fibre mixture was used with cattle, in
three grazing and two semi-restricted experiments, to study the mode
of its excretion, the possibility of using it in a once-daily dosing and
grab-sample regime to estimate fecal output and in a field experiment
to test a hypothesis involving the measurement of forage intake. The
cattle consumed forages available in the sagebrush-bunchgrass region
of Eastern Oregon, in which region the experiments were conducted.
Cr₂0₃-Cellulose was fed to groups of three steers grazing immature
crested wheatgrass, (Agropyron desertorum) in Experiment 1,
or when it was mature along with regrowth in Experiment 2, either
once a day at 8 a.m. or twice daily at 8 a.m. and 4 p.m. Twice a day
grab sampling was carried out from 3-18 days after commencement
of dosing with total collections from days 3-8 and 13-18. Estimated
fecal outputs based on fecal grab sample concentrations at 8 a.m. alone, or the mean of 8 a.m. and 4 p.m. values were calculated in both experiments.
Cr₂0₃ recoveries in Experiment 1 were low, ranging from 71.1-85.4 percent, with individual animals varying little between collection
periods. Estimated fecal dry matter output was high in both groups
for both collection periods and both sampling time methods, ranging
from 115.7-187.3 percent. Standard errors of the mean (S.E.)
were high in the 8 a.m. group in both collection periods, though not
in the twice-daily group. Recoveries in Experiment 2 varied from
94.9-107.6 percent with an overall mean of 100.8 percent. The ratio
of estimated fecal dry matter to that collected had high S.E.'s in
the first period but gave the following results in the second period:
84.3 percent ± 4.5 percent S.E. for 8 a.m. dosing and sampling;
95.0 percent ± 1.5 percent for 8 a.m. and 4 p.m. dosing with 8 a.m.
sampling; 97.1 percent ± 3.8 percent for 8 a.m. dosing and 8 a.m.
and 4 p.m. sampling and 95.6 percent ± 2.0 percent for 8 a.m. and
4 p.m. dosing and sampling.
The four-hourly Cr₂0₃ excretion curve of two groups of two
long yearling heifers, two months pregnant, having continued access
to flood meadow hay, was established by either once or twice daily
dosing. The group dosed, once daily showed a relatively regular diurnal
pattern, the twice-daily dosed group less so. The ratio of 8 a.m.,
and mean of 8 a.m. and 4 p.m. fecal Cr₂0₃ levels to daily mean four-hourly
levels was established over a five-day period and showed a very close relationship to percentage estimates obtained in Experiment 2 for the 8 a.m. dosed and sampled group and to a slightly lesser
extent to the other three groups.
The excretion curve from a single ten gram dose of Cr₂0₃ as
Cr₂0₃-Cellulose in two steers showed appreciable Cr₂0₃ in the
feces within ten hours, a peak from approximately 18-26 hours in
the better steer and levels near the limit of analytical accuracy from
three to five days.
The hypothesis, that poorer growth observed from forced feeding
of common salt late in the grazing season was due to depressed
forage intake, was rejected, using Lancaster's fecal nitrogen method
for determining digestibility and once-daily Cr₂0₃ dosing and sampling
with corrections obtained from Experiment 2 for fecal output to
measure forage intake.
Grab sample Cr₂0₃ concentration was significantly higher in
the morning sample than the afternoon in all experiments. Coefficients
of variation were higher in the morning for once daily dosing
and higher in the afternoon in twice daily dosing.
A series of 12 animal experiments and two simplified laboratory
experiments were used to determine whether small nylon or
cellulose acetate bags placed in the rumen could be passed through
the alimentary tract and used as a possible method of measuring
over-all forage digestibility. Bags tied to the fistula bung by nylon line were recovered intact
at ten days.
Rumen evacuation in cattle showed that nearly all bags placed
free in the rumen had disappeared by three days with evidence of regurgitation
on three occasions and only two free, intact bags. Sheep
experiments by dosing and direct surgical placement in the rumen
confirmed that regurgitation occurred. In a final slaughter experiment
colored polyethylene and glass beads showed most, if not all,
bags had been broken before reaching the reticulo-omasal orifice.
All experimental observations on the fate of the bags are consistent
with the following explanation. The bags in the rumen are
subject to regurgitation; they cannot leave the rumen until this happens,
following which the fragments are swallowed and are of a specific
gravity and size that ensures their passage through the reticulo-omasal
orifice. However, they are then dissolved in the acid environment
of the lower stomachs. Although the problems of using the bag
technique appear insurmountable, the manner of bag movements is
believed to be fully understood.