THE USE OF NEAR-INFRARED REFLECTANCE SPECTROSCOPY ON DRIED SAMPLES TOPREDICT BIOLOGICAL PARAMETERS OF GRASS-SILAGE

This study was undertaken to explore the accuracy of Near Infrared Ref lectance Spectroscopy (NIRS) for the prediction of in vivo OMD (%) and voluntary intake (g/kg W-0.75) measured through sheep and cattle resp ectively. A population of 136 grass silages representing a wide range in chemical and biological parameters was used in this investigation, The dried milled silage samples were scanned at 2 nm intervals over th e wavelength range 400-2500 nm and the optical data recorded as log 1/ Reflectance (log 1/R). The paper examines three multivariate regressio n techniques: modified partial least squares (MPLS), principal compone nt regression (PCR) and stepwise multiple linear regression (SMLR) and investigates the effect of spectral pretreatment using Ist and 2nd or der derivatization with and without three scatter correction procedure s: standard normal variate and detrending (SNV-D), normal multiplicati ve scatter correction (NMSC) and weighted multiplicative scatter corre ction (WMSC), to optimize accuracy of prediction. The optimum mathemat ical treatment was selected by minimizing the standard error of predic tion (SEP) of a blind validation set using a calibration and validatio n set of 90 and 46 respectively, The optimum methods were for in vivo organic matter digestibility (OMD), the stepwise regression procedure using Ist derivatization with a scatter correction (SEP 2.4%, R-2 0.87 ) and for intake the MPLS regression technique again using Ist derivat ization and a scatter correction (SEP 4.77 g/kg W-0.75, R-2 0.79). Com parison of three wavelength ranges (1100-2500 nm, 700-2500 nm and 400- 2500 nm) on the effect of calibration performance for OMD and intake s howed little improvement from extending the range beyond 1100-2500 nm. (C) 1997 Elsevier Science B.V.