| Summary: | This research program was designed to meet three objectives. The first was to ascertain
the feasibility of using near infrared reflectance spectroscopy (NIRS) to predict ruminal
degradability of dry matter (DM) and crude protein (CP) in corn silage (CS) and CP
degradability in grass silage (GS) as determined by the in situ technique. The second objective
was to develop calibration models to predict intestinal disappearance of DM and CP in CS and
intestinal digestibility of CP in GS as determined by the mobile bag technique. The last
objective was to investigate the feasibility of using NIRS to predict the essential amino acid
(AA) composition of CS and GS.
In situ data showed substantial variation in soluble and degradable DM and CP fractions
as well as AA composition of CS. Based on the RPD statistic used to evaluate calibration
equations, NIRS provides a viable option for the prediction of soluble DM and CP for CS,
effectively degraded CS CP and CS CP disappearance from the intestinal and total digestive
tract. It was not possible to produce robust calibration equations to predict rates of CS DM or
CP degradability. Further study is required to ascertain the usefulness of NIRS in predicting AA
composition of CS.
Interpretation of spectral data showed that DM solubility and degradability of CS is
linked to N-H bonding. There was a strong relationship between soluble DM, potentially
degradable DM and effective degradability of CS CP. A review of the major wavelengths used
in each calibration model indicated that fiber did not play a major role in CS DM digestibility.
For the GS study, samples were classified according to increasing content of neutral
detergent fiber (NDF) as this constituent is related to plant maturity. The content of soluble CP
in GS significantly (P<0.01) decreased with increasing maturity but there was no significant
difference (P>0.05) in potentially degradable CP. Likewise the rate of degradation of the
potentially degradable CP fraction did not change according to NDF content. The amount of
nominally undegradable CP from GS significantly (P<0.01) increased with advancing maturity
but there was no difference in intestinal digestibility of ruminally undegradable CP according to
NDF content. Likewise, there was no difference in essential AA content, expressed on a CP
basis, due to stage of maturity.
Ruminally undegraded CP was inversely related to CP ruminal disappearance after 12 h
and/or 24 h incubation. Pearson correlation coefficients were -0.83 and 0.86, respectively.
NIRS was not successful in predicting CP solubility or degradability fractions for GS as
determined by the in situ technique. Prediction of essential AA content of GS was promising as
RPD statistics for each equation, except Met and Lys, approached 2.3.
This thesis presents data for the development of several NIRS calibration models, which
have not been previously explored in the scientific literature. These include models to predict
intestinal digestibility as well as AA composition of forage. The concluding chapter presents
recommendations for experimental methodology as well as for future research in the area of
NIRS model development.
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