|Abstract or Summary
- Digestibility experiments were carried out with dairy heifers to
determine the digestibility of orchard grass, Dactylis glomerata, and
also to evaluate the accuracy of various indicator techniques in pasture
digestibility experiments. Chromic oxide was used as an external
indicator to predict fecal dry matter output in three digestion
trials. Cut grass was fed in one of the trials and corn silage in the
other two. The internal indicators fecal nitrogen and protein of feed
and feces were studied in two of the trials in which one conventional
and one grazing trial were involved. The experimental animals consisted
of six approximately two year old Holstein heifers and six
Jersey heifers of the same ages. All animals were in about the fifth
month of pregnancy.
In the experiments, five grams of chromic oxide in gelatin capsules
were fed to the animals twice a day at 7 A.M. and 4 P.M.
Solka-floc, which is a pure cellulose material, was used as a carrier
for chromic oxide. Fecal grab samples were collected from the rectum
of grazing animals at 6 A.M. and 4 P.M. The chromic oxide recoveries
in the feces of the stall fed animals fed orchard grass ranged
from 98.4 to 99.2 percent, averaging 98.8 percent. The average
difference between the predicted and actual fecal dry matter output
was 23.1 g. This magnitude of difference yielded a 1.01 percent error
of prediction. However, chromic oxide recoveries for the silage
trials were considerably lower, estimated as 79.9 and 74.9 percent
for trials III and IV respectively. These low recoveries of chromic
oxide resulted in a rather high error of prediction of fecal dry matter
output with silages.
The average errors of prediction for the grass forage dry matter
intakes using fecal nitrogen and protein indigestibility techniques
were found to be 1.4 and -6.4 percent, respectively. The respective
differences between the average actual and predicted forage dry matter
intakes were 86.1 and -405.2 g. Based on the results of this
study the fecal nitrogen index technique appears to be superior to the
protein indigestibility technique.
The digestion coefficients of ether extracts were found to be
higher for the conventional trial with pasture than for that of the
grazing trial, while the reverse was true for the nitrogen free extracts.
The average TDN and digestible energy values for orchard grass dry matter in the conventional trial were found to be 67.1 and
68.0 percent, respectively. The difference in estimations of the
TDN and digestible energy values between total collection and fecal
nitrogen technique was 0.5 percent, which may be regarded as a reasonable
error in digestibility experiments. The TDN and digestible
energy values of the grazing trial were slightly higher than that of
the conventional trial. The digestible energy determinations were
highly correlated with the calculated TDN values.
It was concluded that chromic oxide and fecal nitrogen may be
used effectively in pasture digestibility experiments. More research
is needed to establish their use as reliable indicators with single feed
stuffs, such as silages, or when combined in complete rations.