Predicting Forage Quality by Infrared Replectance Spectroscopy

Abstract

Near-infrared-reflectance spectra (1.4 to 2.4 µm) were recorded for 87 samples of ground dry forages. Temperate forage species analyzed were alfalfa, tall fescue and alfalfa bromegrass mixtures preserved as hay, silage and fresh frozen forages. Tropical species included bermudagrass and pangola digitgrass. Laboratory analysis of crude protein (CP), acid detergent fiber (ADF), neutral detergent fiber (NDF), lignin (L) and in vitro dry matter disappearance (IVDMD), as well as in vivo digestibility (DMD), dry matter intake (DMI) and digestible energy intake (DEI) were determined for these same samples. Reflectance (R) spectra were recorded as log (1/R) vs wavelength and transformed to the second derivative of log (1/R) vs wavelength for correlation with compositional and nutritional data. Multiple-linear-regression techniques were used to determine the optimum wavelengths for predicting each of the chemical in vitro and in vivo analyses. By use of up to nine wavelengths points for the prediction equations, the correlation coefficients were .99 for CP, .98 for NDF, .96 for ADF, .96 for L, .95 for IVDMD, .88 for DMD, .80 for DMI and .85 for digestible energy intake (DEI). Calibration equations generated from the odd-numbered samples predicted the values for the even-numbered samples within a standard error of ± .95% for CP, ± 3.1% for NDF, ± 5.1% for DMD and ± 7.9 g for DMI. We concluded that infrared reflectance has the potential for use in rapid evaluation of forage quality.