Effect of Anaerobic Calcium Oxide Alkalization on the Carbohydrate Molecular Structures, Chemical Profiles, and Ruminal Degradability of Rape Straw

SIMPLE SUMMARY: Rape straw has been used as livestock feedstuff in many countries, but the low digestibility caused by the high degree of lignification has limited its application in ruminant diets. Numerous techniques have been employed to enhance the nutritional quality of rape straw, including physical, chemical, and microbial methods. Among these, anaerobic alkaline storage is particularly effective in improving the straw’s nutritional value and preventing mold growth. To improve the utilization efficiency of rape straw, anaerobic calcium oxide alkalization was conducted, and advanced molecular spectroscopy was applied, to detect the internal molecular structural changes. The calcium oxide treatment increased the contents of soluble fiber, improved the ruminal degradability of neutral detergent fiber and acid detergent fiber, and decreased the contents of indigestible fiber. Alterations in cellulosic compounds’ spectral regions were highly correlated with the differences in carbohydrate chemical constituents and the ruminal digestibility of rape straw, which indicated that the infrared techniques could be used to evaluate the carbohydrate nutritive properties. The results of this study showed that calcium oxide treatment and anaerobic storage changed the molecular characteristics and improved the nutritive properties of rape straw. ABSTRACT: To improve the utilization efficiency of rape straw, anaerobic calcium oxide (CaO) alkalization was conducted, and advanced molecular spectroscopy was applied, to detect the internal molecular structural changes. Rape straw was treated with different combinations of CaO (3%, 5%, and 7%) and moisture levels (50% and 60%) and stored under anaerobic conditions. We investigated the carbohydrate chemical constituents, the ruminal neutral detergent fiber (aNDF) and acid detergent fiber (ADF) degradation kinetics, and the carbohydrate molecular structural features. CaO-treated groups were higher (p < 0.05) for ash, Ca, non-fiber carbohydrate, soluble fiber, and the ruminal degradability of aNDF and ADF. In contrast, they were lower (p < 0.05) for the contents of aNDF, ADF, and indigestible fiber. With CaO levels rising from 3% to 7%, the content of aNDF and ADF linearly decreased (p < 0.05). CaO treatment and anaerobic storage changed the molecular characteristics, including structural parameters related to total carbohydrates (TC), cellulosic compounds (CEC), and structural carbohydrates (STC). Alterations in cellulosic compounds’ spectral regions were highly correlated with the differences in carbohydrate chemical constituents and the ruminal digestibility of rape straw. In summary, CaO treatment and anaerobic storage altered the molecular structural parameters of carbohydrates, leading to an enhancement in the effective degradability (ED) of aNDF and ADF in rape straw. From the perspective of processing cost and effectiveness, 5% CaO + 60% moisture could be suggested as a recommended treatment combination.