Prediction of phenolics and tannins in forage legumes by near infrared reflectance

Near infrared (NIR) spectroscopy calibrations for measures of tannins and nutritive value were made on a set of 40 hays and straws of Vicia and Lathyrus spp. by the modified partial least squares (MPLS) method and were evaluated by cross-validation. They successfully predicted, in the dry matter, 4.6-34.1 g kg-1 total phenolics with a cross-validation R2 of 0.95 and a SECV of 1.68 g kg-1, 1.3-23.1 g kg-1 total tannins (R2 = 0.89, SECV = 1.84 g kg-1) and 0.5-30.3 g kg-1 condensed tannins (R2 = 0.93, SECV = 2.34 g kg-1). In multiple regression and MPLS calibrations, a wavelength close to 2.144 μm was common to all measures of tannins, and was attributed to condensed tannins and its flavanoid precursors. The biological activity of tannins on rumen microbes, measured as a 0-6.9% effect on gas production with rumen liquor in vitro, was less precisely predicted by MPLS (R2 = 0.49, SECV = 1.49%). The biological activity per gram of chemical tannins could not be predicted by NIR spectroscopy in the material studied. Acid detergent fibre, neutral detergent fibre, crude protein and gas production in vitro were predicted with R2 = 0.95 to 0.96 (SECV = 18.2, 24.8, 10.1 g kg-1 or 7.2 mL g-1).