Comparing the Use of Handheld and Benchtop NIR Spectrometers in Predicting Nutritional Value of Forage
Authors: Rukundo Isaac R , Danao Mary-Grace C , Mitchell Robert B , Masterson Steven D , Weller Curtis L 
Published: February 2021

Highlights

A transportable spectrometer performed similarly to benchtop spectrometers to predict forage quality.

Absorption bands in the second and third overtone regions were used to predict forage quality with ample accuracy.

A low-cost handheld spectrometer was useful for routine screening of forage for nitrogen content.

Abstract. Assessing the nutritional composition of animal feed and forage materials is important to achieve high animal productivity and wellness. Precision nutrition programs that use NIR technology can determine the nutritional composition of feed and forage quickly and simply, generating actionable information such as total nitrogen (N), acid detergent fiber (ADF), neutral detergent fiber (NDF), and acid detergent lignin (ADL) contents, as well as in vitro dry matter digestibility (IVDMD). Recent advances in optics and microelectronics have allowed for the development of handheld spectrometers that are portable, robust, and user-friendly. However, are the handheld units accurate enough to predict nutritional content of animal feed? In this study, the performance of two handheld NIR spectrometers to predict the nutritional content of forage based on N, ADF, NDF, ADL, and IVDMD was evaluated by comparing them to two benchtop NIR spectrometers often used in feed and forage analysis. The forage samples comprised switchgrass (Panicum virgatum L), big bluestem (Andropogon gerardi), and Indiangrass (Sorghastrum nutans). The first handheld spectrometer covers 780-2500 nm with a spectral interval (??) of 1 nm, while the second handheld spectrometer is a palm-sized smartphone spectrometer covering 900-1700 nm with ?? = 4 nm. The benchtop spectrometers both cover 400-2500 nm with ?? = 2 nm. Forage samples were scanned on each spectrometer and divided into calibration (n = 143) and validation (n = 35) sets. Partial least squares (PLS) regression was used to calibrate all spectrometers using mean-centered spectral data that had been preprocessed using Savitzky-Golay first derivative (SG1) or second derivative (SG2) algorithm with 9-63 smoothing points. Results showed that PLS models that best predicted N using the benchtop spectrometers had lower standard error of prediction (SEP = 1.24-1.28 g kg-1) and higher ratio of prediction to deviation (RPD = 3.66-3.78) compared to the models developed based on spectra collected from the handheld spectrometers (SEP = 1.46-1.78 g kg-1; RPD = 2.39-2.84). ADF, NDF, and ADL were variable and generally poorly predicted using spectra from the benchtop spectrometers (SEP = 10.02-33.19 g kg-1;RPD = 1.71-2.24), and even more so using the handheld spectrometers (SEP = 10.63-32.57 g kg-1;RPD = 1.64-2.47). Predicting IVDMD was similar for both sets of benchtop (SEP = 40.00-41.73 g kg-1; RPD = 2.24-2.34) and handheld (SEP = 34.46-40.84 g kg-1; RPD = 2.29-2.72) spectrometers. These results show that the handheld devices can be used for screening of forage samples based on N, which is a closely monitored component in animal feed and forage, as well as IVDMD, an important forage quality index. Keywords: Forage, Portable spectrometer, Spectroscopy, Screenin, Ruminant nutrition.