Predicting Composition, Intake, and Digestibility of Nutrients in Grazing Cattle Using Near Infrared Spectroscopy (NIRS) of Feces

The objective of this study was to determine the potential of near infrared-spectroscopy (NIRS) scanning of feces to predict fecal composition, diet digestibility, and intake in beef cattle fed high forage diets. Beef heifers were fed 12 different forage-based diets (> 95% forage dry matter basis) in 3 total collection digestibility studies, resulting in individual fecal samples and related spectra (n = 135) corresponding to nutrient, apparent total tract digestibility (aTTD), and intake data. Dried and ground fecal samples collected from each animal were scanned using a FOSS DS2500 scanning monochromator (FOSS, Eden Prairie, MN). Spectra were mathematically treated for scatter correction and modified partial least squares (MPLS) regression was performed to develop equations with acceptable accuracy and low error. The standard error of cross validation (SECV), and coefficient of determination for cross validation (R²_cv) were used to evaluate the accuracy of calibration equations. Prediction equations were developed for fecal composition [organic matter (OM), nitrogen (N), neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL), undigestible NDF (uNDF), calcium (Ca), and phosphorus (P)], digestibility [DM, OM, NDFD, N], and intake [DM, OM, NDF, N, uNDF]. The calibrations for fecal OM, N, NDF, ADF, ADL, uNDF, Ca, P resulted in R² CV between 0.81 and 0.97 and SECV of 0.84, 0.60, 1.55, 0.47, 1.68, 0.15, and 0.06, respectively. Accuracy of equations predicting intake of DM, OM, N, NDF, ADL and uNDF resulted in R² CV values between 0.59 and 0.91, SECV for intake (kg/d) of 1.12, 1.10, 0.02, 0.69, 0.06, 0.24, respectively, SECV for intake % body weight (BW) between 0.00 and 0.16; and SECV for g/kg BW^0.75 between 0.60 and 0.86. Digestibility calibrations for DM, OM, NDF, and N resulted in R² CV ranging from 0.65 to 0.74 and SECV from 2.20 to 2.82. This study confirms the potential of NIRS to predict fecal chemical composition, as well as digestibility and intake of cattle fed high forage diets. Future steps include expansion and further validation of the calibration equations with spectra from varying grazing systems.

Key words: near-infrared spectroscopy, feces, fecal composition, apparent total tract digestibility, intake, beef, forage.

Presented at the 2022 Animal Nutrition Conference of Canada. For information on the next edition, click here.