UBC Theses and Dissertations

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UBC Theses and Dissertations

Prediction of dry matter, crude protein degradability, and amino acid composition of corn silage and grass silage by near infrared reflectance spectroscopy (NIRS) Swift, Mary Lou


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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