THE USE OF NIRS TO PREDICT THE CHEMICAL-COMPOSITION AND THE ENERGY VALUE OF COMPOUND FEEDS FOR CATTLE

By means of a scanning monochromator and partial least-squares analysi s, near-IR reflectance spectroscopy (NIRS) calibrations were developed to predict the chemical composition and the energy value of two diffe rent sets of compound feeds for cattle. The first set contained 179 co mpounds of heterogeneous nature, for which the energy value was calcul ated from in vivo digestibility. The second set consisted of 163 comme rcial dairy compounds for which the energy value was predicted from en zymatic digestibility. Spectral and reference data were highly correla ted for all parameters, except for ash. For the first set, the root me an square error of prediction (RMSEP) amounted to 0.5% (percentage uni ts) for moisture, 1.4% on dry matter basis (DM) for crude protein, 1.4 % on DM for crude fibre, 0.7% on DM for crude fat, 2.1% for in vivo di gestibility, 0.37 MJ kg-1 DM for metabolizable energy (ME) and 0.27 MJ kg-1 DM for net energy lactation (NEL). Prediction of ME and NEL with regression equations based on enzymatic digestibility was somewhat mo re accurate, with an RMSEP of 0.30 MJ kg-1 DM and 0.22 MJ kg-1 DM, res pectively. For the more homogeneous second set, the RMSEP was lower fo r all parameters: 0.3% for moisture, 1.1% on DM for crude protein, 0.9 % on DM for crude fibre, 0.3% on DM for crude fat, 1.3% for enzymatic digestibility, 0.30 MJ kg-1 DM for ME and 0.18 MJ kg-1 DM for NEL. It was proved that calibrations derived from energy values predicted from enzymatic digestibility were hardly less accurate than those derived from in vivo data. Calibrations based on the currently used NIRS instr ument with 19 filters gave similar results to those based on the full spectrum for moisture, crude protein and crude fat, were less accurate for crude fibre, and clearly failed for energy evaluation. It was con cluded that NIRS can be used as a screening method for the control of the chemical composition and the energy value of compound feeds for ca ttle.