The use of near infrared spectroscopy to investigate the composition of silages and the rate and extent of cell-wall degradation

Samples of 25 grass silages and of one maize, one lucerne and one whole cro p wheat silage, of known digestibility, chemical composition and cell-wall degradability, were scanned on an near infrared spectrometer (NIRS). Also s canned were samples of the cell-wall (i.e. neutral detergent fibre (NDF)) f raction of the silages and the cell-wall residues produced by incubating th e silage in buffered rumen fluid for 3, 8, 16, 24, 45 or 72 h and boiling w ith neutral detergent solution. The data points were transformed by the sta ndard normal variate and detrending (SNV-D) procedure. Difference spectra w ere obtained by subtracting the spectrum of the 72 h residue from those of each of the 3, 8, 16, 24 and 45 h residues. The aim was to investigate the extent to which MRS may be useful as a means of learning more about the dig estibility and composition of silages and predicting the rate and extent of cell-wall degradation. The difference spectra of all the silages examined were of similar pattern, with prominent positive regions, indicating components of high degradabili ty at similar to 1430-1620 and 1960-2230 nm, a prominent negative region, i ndicating components of low degradability, at 2230-2400 nm, and other negat ive regions at 1140-1430 and 1620-1820 nm. Among the 25 grass silages, the spectral regions with the strongest positive correlation with digestibility included those around 1676 and 2228 nm, which corresponded approximately w ith regions of strong negative correlation with lignin (1672 and 2246 nm) a nd NDF (1680 and 2214 nm). There were spectral regions of strong positive c orrelation with fractional rate of cell-wall degradation h(-1), indicated b y c, around 1684 and 2214 nm, which corresponded with regions of strong neg ative correlation with silage MDF (1680 and 2214 nm); there were regions of strong negative correlation with c at around 1414 and 1922 nm, which corre sponded with regions of strong positive correlation with silage NDF (1406 a nd 1922 nm). The array of information provided by near infrared (NIR) spect ra has the potential to enhance understanding of digestion and cell-wall de gradation. (C) 2000 Elsevier Science B.V. All rights reserved.