Variations and correlations of shearing force and feed nutritional characteristics of millet straw

Abstract: In order to find the variations and correlations of shearing force and feed nutritional characteristics of millet straw, temporal dynamics of shearing force, compressive strength, morphological index, and nutritional content of millet straw were investigated after grain fully matured in this study. Results showed that the unit diameter shearing force, compressive strength, cellulose content, hemicellulose content, and lignin content increased in different straw parts with advancing maturity time. However, the linear density, moisture content and crude protein content decreased. There was negative relationship between unit diameter shearing force and moisture content, and between unit diameter shearing force and linear density (R2≥0.903). In the meanwhile, the unit diameter shearing force was positively related with cellulose content, hemicellulose content, and lignin content (R2≥0.845), but there was no relationship between unit diameter shearing force and crude protein content (P>0.05). The shearing force increased from upper part to proximal root part of plant in different sampling times (P<0.05), and the shearing force was positively correlated with the equivalent diameter and cross-sectional area (R2≥0.916). This research showed that the relative errors between verification test value and predicted value were not more than 6.48% of forage characteristics of millet straw, so that the regression models were feasible. Further, measuring shearing force is an efficient method to evaluate morphological index and nutritional content, providing the potential for enhancement of voluntary feed intake of millet straw. It was presented that the unit diameter shearing force of the part above the middle section was significantly less than that of the proximal root part of millet straw (P<0.05), so that above the middle part of millet straw should be selected as ruminant feed. Meanwhile, timely harvesting after grain fully matured can avoid the decrease of feed value. This study can provide a reference for improving the forage utilization of millet straw.