Effects of herbal medicine residues on the fermentation characteristics and microbial community of maize stover

Every year, China generates 35 million tons of herbal medicine residues, most of which are directly discarded or burned, causing problems such as groundwater pollution, air pollution, and global warming. These residues have the characteristics of feed and medicinal materials, and are rich in various nutrients and bioactive substances, such as cellulose, proteins, polysaccharides, flavonoids, phenolic compounds, essential oils, and organic acids. Due to the low cost, wide availability, and good efficacy and few side effects of these natural resources, they have increasingly attracted attention. Therefore, it is crucial to develop technologies for the sustainable utilization of biomass resources. With the development of modern agriculture and advancements in agricultural breeding science and technology, the health of livestock has received increasing attention. In particular, the unreasonable use of antibiotics has led to many problems, such as antibiotic-resistant bacteria and antibiotic residues, which seriously threaten the health of animals and humans. Therefore, in recent years, the application of herbal medicine residues in animal health care and disease prevention has received more and more attention. While China's corn yield has steadily increased, a large amount of corn straw resources has been generated. According to statistics, maize stover accounts for 31.45% of the total straw resources of China's grain crops. However, these straw resources have not been well utilized. The utilization of maize stover as silage is one of the main ways of its resource utilization. However, during anaerobic fermentation, due to harmful microorganisms such as Bacillus, Clostridium, and enterobacteria to the surface of maize stover and without any treatment, it is difficult to produce high-quality silage. In addition, maize stover has a high cellulose content, mainly including acid detergent fiber and neutral detergent fiber, which are difficult for ruminants to digest and absorb. However, to the best of our knowledge, there is no information on the regulation of the nutritional value and quality of maize stover silage during fermentation using herbal medicine residues. This study aims to improve the efficient utilization of herbal medicine residues and alleviate environmental pollution, this study investigated the effects of adding 11 types of herbal medicine residues on cellulose degradation, fermentation quality, and microbial community structure in maize stover silage. The tested herbal medicines included Bupleurum falcatum L. (BF), Astragalus memeranaceus F. (AM), Acanthopanar gracilistμlus W. (AG), Codonopsis pilosula F. (CPF), Taraxacum mongolicum Hand (TMH), Common Yam R. (CY), Salvia miltiorrhiza B. (SM), Plantago asiatica L. (PA), Saposhnikovia divaricata T. (SD), Spatholobus suberectus Dunn (SSD) and Poria cocos S. (CP). Compared with the control group, the herbal medicine residue treatments significantly increased the contents of lactic acid, acetic acid, propionic acid, and 2,3-butanediol to 35.13-45.78, 35.02-53.81, 6.35-8.57, and 1.31-1.97 g/kg, respectively, while decreasing ethanol and 1,2-propanediol contents to 0.44-1.52 and 0.42-1.17 g/kg. Additionally, all herbal medicine residue groups exhibited lower NH₃-N contents (1.77-3.07 g/kg) than the control group, with the exception of the SM and SSD treatments. Compared with the control, corn straw silage treated with BF and AG displayed lower contents of acid detergent fiber (ADF) and neutral detergent fiber (NDF). In the groups treated with herbal medicine residues, the relative abundance of Lactiplantibacillus plantarum and Levilactobacillus brevis increased to 30.06%～65.09% and 4.22%-27.29%, respectively. The relative abundance of Bacillus licheniformis and Bacillus subtilis declined, dropping to 0-1.11% and 0-1.23% correspondingly. Among all herbal medicine residues treatment groups, the AG and BF groups exhibited the optimal performance, which could not only degrade cellulose but also enhance the fermentation quality of maize stover silage via microbial regulation. Overall, exploring the effects of herbal medicine residues on maize stover fermentation highlights their promising application potential in practical agricultural production.