Fecal NIRS equations for predicting diet quality of free-ranging cattle.

Abstract

The usefulness of near infrared reflectance spectroscopy (NIRS) for predicting diet quality of free-ranging cattle through fecal analysis was examined. Diet samples were obtained with esophageal fistulated steers; subsequently, study areas were grazed with nonfistulated lactating and dry cows to provide fecal samples representing differing forage diet quality. Diet samples, which were analyzed by conventional laboratory procedures for in vivo corrected digestible organic matter (DOM) and crude protein (CP), provided dependent variable reference data while fecal sample spectra provided independent variable data for development of NIRS predictive equations by stepwise regression. Equations were developed from a data set at one location with subsequent equation development using expanded data ranges obtained by adding samples from a second location. Standard errors of calibration (SEC) and validation (SEV) for the DOM equation developed from the expanded data range were 1.66 and 1.65, respectively; these values were nearly equivalent to the laboratory standard error (SEL) of 1.68. SEC and SEV for the CP equation developed from the expanded data range were 0.89 and 0.93, respectively, compared to the 0.44 SEL. Coefficients of determination for DOM and CP equations were 0.80 and 0.92, respectively. These statistical parameters developed from fecal spectra to predict forage diet quality are equal to or better than statistics reported in the literature for NIRS equations developed using forage spectra. Furthermore, equation standard errors were within acceptable limits for NIRS calibrations. No effects of physiological stage of animals on calibration were noted in this study. Results are interpreted to indicate that prediction of diet DOM and CP of free-ranging herbivores can be accomplished with NIRS fecal analysis to a degree of precision equivalent to conventional laboratory diet analyses.