Comparison of two internal markers and near-infrared spectroscopy (NIRS) for predicting nutrient digestibility in beef cattle offered diets varying in forage quantity and quality

The objective of this study was to evaluate acid detergent lignin (ADL), amylase-treated ash-corrected undigestible neutral detergent fiber (uNDFom), and near-infrared spectroscopy (NIRS) of feces as methods to estimate the digestibility of beef cattle diets varying in forage quantity and quality. Five digestibility studies provided individual fecal samples and corresponding apparent total tract digestibility (TTD) of nutrients ( n = 229). An NIRS calibration was expanded with dried and ground samples and calibration performance evaluated using internal cross-validation. Mean fecal recovery of markers were 94.2% (SD ± 15.7%) for ADL and 87.5% (SD ± 11.1%) for uNDFom. The R 2 between NIRS and TTD was greater than 0.83 except for ADF digestibility ( R 2 = 0.63); however, R 2 < 0.78 for internal markers. Concordance correlation coefficients between NIRS and TTD were greater than 0.77, between 0.63 and 0.82 for ADL, and 0.26 to 0.78 for uNDFom. Correction bias (Cb) was greater than 0.76 except for ADF digestibility (Cb = 0.58) as estimated by uNDFom. The mean square error of prediction for NIRS predicted digestibility were lower (<10.7) than those estimated by internal markers. Digestibility predictions from NIRS were more accurate and precise than estimated using the internal makers.