Effects of compound additives on the quality and microbial diversity of mulberry and navel orange residue mixed silage

The effects of compound bacterial preparations and compound enzyme preparations on the quality and microbial diversity of mulberry and navel orange residue mixed silage were investigated. Four experiment groups were formed: control group (group CK, no addition), compound bacterial preparation group (group J, 0.1% Lactobacillus plantarum and 0.05% Bacillus subtilis), compound enzyme preparation group (group M, 0.01% cellulase and 0.1% xylanase), and compound bacterial enzyme preparation group (group JM, 0.1% Lactobacillus plantarum, 0.05% Bacillus subtilis, 0.01% cellulase, and 0.1% xylanase). There were three replicates per group, and the silage fermentation time was 60 days. Compared with those of the CK group, the dry matter and crude protein contents of the J and JM groups significantly increased (P < 0.05); the neutral detergent fiber content of the J, M, and JM groups significantly decreased (P < 0.05). The acid detergent fiber content of the M and JM groups significantly decreased (P < 0.01), whereas the acid detergent fiber content of the J group had no significant change (P > 0.05). Compared with that of the CK group, the pH of the J, M and JM groups significantly decreased (P < 0.01); although the ammonia nitrogen content of the J and JM groups significantly decreased (P < 0.01), there was no significant change in group M (P > 0.05). The lactic acid content of groups J, M, and JM significantly increased compared with that of the CK group (P < 0.01). The acetic acid content of group M was the highest, whereas the propionic acid content of group JM was the lowest. Butyric acid was not detected in any group. The dominant phylum of bacteria in each group was Firmicutes, and its relative abundance was the highest in group JM. This was followed by Proteobacteria, which had the highest relative abundance in the CK group. The dominant bacterial genera in groups CK and M were primarily Lactobacillus, Enterobacter, and Klebsiella, whereas those in groups J and JM were Lactobacillus, Bacillus, and Weissella. In conclusion, adding compound bacterial preparations and compound enzyme preparations separately can improve the nutrient and fermentation quality and the structure and composition of microbial flora; however, the silage effect of the combined addition of compound bacterial enzyme preparations is better.