Estimates of Intake and Quality of Grazed Range Forage by near Infrared Reflectance Spectroscopy

Abstract

Near infrared reflectance spectroscopy (NIRRS) was used to estimate organic matter intake of, and chemical components in, forages grazed by cattle on arid and semi-arid rangeland in New Mexico. Twenty-one samples of grazed forage were composited from over 150 specimens individually collected in esophageal fistulated cattle. These represented 21 sets of valid measures of organic matter intake (OMI). Spectra of these samples were obtained with a scanning monochromator interfaced with a minicomputer and evaluated as log (1/R), Δ log (1/R) and Δ² log (1/R) in relation to chemical components and OMI. Wavelengths best related to chemical components and OMI were selected by a modified stepwise multiple regression program. Wavelengths most useful in calibration were 1.410 and 2.214 µ for OMI; 2.135, 2.043 and 2.259 µ for crude protein content (CP); 1.687, 2.259 and 1.811 µ for acid-detergent fiber content (ADF); and 2.326 and 2.086 µ for acid detergent lignin content (ADL). OMI and ADL were best related to spectral data as Δ log (1/R), whereas CP and ADF were best related to spectral data as Δ log (1/R). For the calibration equations, standard errors of estimates were ± 9.6 g·;d^-1·;(kg BW^.75)^-1 for OMI; ± .37% for CP; ± 1.26% for ADF; and ± .67% for ADL. Corresponding R² values were .72, .98, .90 and .79. OMI was related to NIRRS as closely as to CP, ADF and ADL. NIRRS promises to be useful in rapid estimates of intake and composition of range forages that vary in plant species constituents.