Effects of corn straw treated with CaO on rumen degradation characteristics and fermentation parameters and their correlation with microbial diversity in rumen

The objectives of this study were to investigate the degradation characteristics and fermentation parameters of corn straw treated with different concentrations of calcium oxide (CaO) and degradation characteristics and fermentation parameters of samples in relation to microorganisms diversity in the rumen. Corn straw with 60 % moisture were treated with four concentrations of CaO (0 %, 3 %, 5 %, and 7 % of dry straw weight) respectively: i) The nylon bag technology method was used in estimating the rumen effective degradability, and each treatment was performed eight times. Then, the degradability of dry matter (DM), neutral detergent fiber (NDF) and acid detergent fiber (ADF) were determined by taking nylon bags from rumen at 0 h, 4 h, 8 h, 12 h, 24 h, 48 h and 72 h, respectively. ii) The fermentation parameters of corn straw were measured by rumen simulation technology in vitro. The mixture was measured at different times (6 h, 12 h, 24 h and 72 h) for the determination of ammonia nitrogen (NH₃–N), volatile fatty acids (VFAs) indexes and rumen microbes. iii) The free online platform of Majorbio Cloud Platform was used in evaluating microbe diversity, abundance, and taxonomic composition in the rumen. Species difference analysis was designed, each treatment had three replicates, and 48 samples in total were used. iv) The correlations among effective degradability, fermentation indexes, and rumen microorganisms of corn straw treated by CaO were analyzed by means of an online platform. The results showed that i) the effective rumen degradability of corn straw treated with CaO significant differed among treatments (P < 0.01). The degradability of DM, NDF, and ADF in 7 % and 5 % treatments were higher than that in other treatments (P < 0.01). Soluble and rapidly degraded components in corn straw had significant higher in 5 % and 7 % treatments than in the 0 % and 3 % treatments. ii）The concentrations of acetate, propionate, butyrate, and total VFA at 6 h in vitro had significant differences (P < 0.01) or obvious upward tendency with increasing concentration of CaO. iii) Alpha index analysis revealed that rumen microorganisms diversity and abundance obviously decreased from 0 % to 7 % treatment in 6 h fermentation. Rikenellaceae_RC9_gut_group at the genus level decreased in the top 15 species in terms of average abundance (P < 0.01), but the most abundant genus Prevotella_1 had an upward tendency in 6 h incubation (P = 0.066). iv) Correlation analysis demonstrated that Prevotella_1 and Prevotellaceae_UCG-003 had positive correlations with acetate, propionate, total VFA, and DM, NDF, and ADF degradability (P < 0.01). Overall, corn straw treated with CaO at 5 % and 7 % can improve rumen effective degradability and promote the fermentation of corn straw, especially promoting Prevotella_1 enrichment in the straw in a short time. In terms of cost saving, 5 % CaO treatment is the best choice.