Digestibility Analysis of Undried, Unground, and Dry Ground Herbage by Near‐Infrared Reflectance Spectroscopy

Analysis of herbage quality by near‐infrared reflectance spectroscopy (NIRS) usually involves dry ground samples. Costs might be reduced if samples could be analyzed without drying and grinding. Our objective was to test influences of herbage processing treatments on NIRS analytical accuracy. In Exp. 1, grass and legume samples were scanned in fresh or thawed coarse (unground) condition, then fresh subsamples were dried and scanned before and after grinding. In Exp. 2 samples were dried or frozen and thawed, then scanned in coarse condition. Dried samples were then ground and rescanned. In vitro dry matter digestibility (IVDMD) was determined in both experiments for ground samples that were dried without freezing, and in Exp. 2 for samples that were frozen and thawed before drying and grinding. Freezing and thawing reduced digestibility by 7 g kg− 1 for grasses and 33 g kg− 1 for legumes, but the reduction was inconsistent among grass species. Calibrations were developed for pooled and separate grass and legume populations. Analytical accuracy, represented by standard error of cross‐validation (SECV), was similar among grass treatments (SECV ≥ 27 g kg− 1 ), but was higher for dry ground (SECV ≥ 16 g kg− 1 ) than for coarse (SECV ≥ 21 g kg− 1 ) treatments within legume and pooled populations. Coarse samples require less processing, but more replicate scans for spectral repeatability, than dry ground samples. Coarse sample analysis may be acceptable when processing is costly, rapid analyses are required, or when possible compositional alterations due to freezing or drying should be avoided.