Pasture Floristic Composition and Performance of Portable and Benchtop NIRS for Predicting Feces Chemical Composition in Grazing Brown Swiss Heifers

Optimizing livestock production under variable grazing conditions requires rapid and accurate tools to assess forage quality and animal digestive efficiency. Near-infrared spectroscopy (NIRS) offers a fast, reliable, and non-destructive approach for predicting feces chemical composition and indirectly assessing diet quality. This study evaluated pasture floristic composition and the predictive performance of portable and benchtop NIRS instruments for estimating feces chemical composition in grazing Brown Swiss heifers. Floristic composition was assessed in six paddocks, and 96 feces samples were collected for chemical analysis and NIRS prediction. Lolium spp. (31–38%) and Dactylis glomerata (20–37%) were the dominant pasture species. Feces crude protein ranged from 12.39 to 14.08%, ash from 16.15 to 19.59%, NDF from 43.20 to 48.96%, ADF from 31.30 to 37.22%, and IVDMD from 62.09 to 66.20%. Benchtop NIRS performed better for crude protein and ash, with R2CV values of 0.89 and 0.91, respectively. Portable NIRS performed better for NDF, ADF, and IVDMD, with R2CV values of 0.80, 0.76, and 0.73, respectively. Both instruments showed potential for rapid prediction of feces chemical composition in grazing heifers. These findings support the use of NIRS as a practical complementary tool for nutritional monitoring and management of grazing cattle under variable pasture conditions worldwide.