Comparison of In Vitro Dry Matter Digestibility and Cellulase Digestion for Deriving Near Infrared Reflectance Spectroscopy Calibration Equations Using Cool-Season Grasses

Near infrared reflectance spectroscopy (NIRS) has recently become a potentially valuable and reliable tool for analyses of plant samples in forage-breeding programs. The success of NIRS is dependent on identification of appropriate and reliable selection criteria and development of reliable calibration. The objectives of this study were to develop and compare NIRS analysis equations for the in vitro dry matter digestibility of cool-season grasses based on either rumen fermentation (IVDMD) or ceilulase-solubility (CDMD) methods and to determine if NIRS prediction equations developed from these methods would rank selected genotypes in the same order. Breeding nursery samples of smooth bromegrass (Bromus inermis Leyss.) and crested wheatgrasses [Agropyron cristatum (L.) Gaertner and Agropyron desertorum (Fisch) Schultes] were analyzed for IVDMD and CDMD to develop NIRS analysis equations. Forage samples collected at inflorescence emergence from individual genotypes in the nurseries were used to develop a rank comparison of digestibility methods. The IVDMD and CDMD laboratory values were highly correlated (r >--0.95). Five to nine wavelengths were required to develop the NIRS analysis equations. The coefficients of determination (R2) from regression of laboratory values on NIRS spectra were 0.96 or higher for all equations. Validation procedures indicated excellent correlations between laboratory and NIRS estimates. Spearman rank order correlations of IVDMDor CDMDderived NIRS digestibility values of genotypes were >-0.77 for both grasses. At least 15 or more genotypes in the top and bottom 20 were the same with either procedure for both grasses. Near infrared reflectance spectroscopy calibrations for in vitro digestibility based on either IVDMD or CDMD procedures will adequately rank genotypes in cool-season grass breeding programs in a similar order. ~4dditional index words: Smooth bromegrass, Bromus inermis Leyss., Crested wheatgrass, Agropyron cristatutn, ~4gropyron deser-