THE PREDICTION OF INTAKE POTENTIAL AND ORGANIC-MATTER DIGESTIBILITY OF GRASS SILAGES BY NEAR-INFRARED SPECTROSCOPY ANALYSIS OF UNDRIED SAMPLES

A study was undertaken to examine a range of sample preparation and ne ar infrared reflectance spectroscopy (NIPS) methodologies, using undri ed samples, for predicting organic matter digestibility (OMD g kg(-1)) and ad libitum intake (g kg(-1) W-0.75) of grass silages. A total of eight sample preparation/NIRS scanning methods were examined involving three extents of silage comminution, two liquid extracts and scanning via either external probe (1100-2200 nm) or internal cell (1100-2500 nm). The spectral data (log 1/R) for each of the eight methods were ex amined by three regression techniques each with a range of data transf ormations. The 136 silages used in the study were obtained from farms across Northern Ireland, over a two year period, and had in vivo OMD ( sheep) and ad libitum intake (cattle) determined under uniform conditi ons. In the comparisons of the eight sample preparation/scanning metho ds, and the differing mathematical treatments of the spectral data, th e sample population was divided into calibration (n = 91) and validati on (n = 45) sets. The standard error of performance (SEP) on the valid ation set was used in comparisons of prediction accuracy. Across all 8 sample preparation/scanning methods, the modified partial least squar es (MPLS) technique, generally minimized SEP's for both OMD and intake . The accuracy of prediction also increased with degree of comminution of the forage and with scanning by internal cell rather than external probe. The system providing the lowest SEP used the MPLS regression t echnique on spectra from the finely milled material scanned through th e internal cell. This resulted in SEP and R-2 (variance accounted for in validation set) values of 24 (g/kg OM) and 0.88 (OMD) and 5.37 (g/k g W-0.75) and 0.77 (intake) respectively. These data indicate that wit h appropriate techniques NIRS scanning of undried samples of grass sil age can produce predictions of intake and digestibility with accuracie s similar to those achieved previously using NIRS with dried samples. (C) 1998 Elsevier Science B.V.