Effects of different additives and chopping lengths on the biosafety of Sophora Davidii silage

Antibiotic resistance genes (ARGs), mobile genetic elements (MGEs), and virulence factors (VFs) represent growing threats to global public health. Sophora davidii silage is a common feed in livestock production, may potentially serve as a reservoir and vector for the dissemination of these genetic determinants. The biosafety risks associated with Sophora davidii silage remain poorly evaluated. Consequently, mitigating these risks through improved processing techniques has become an urgent priority. This study systematically elucidates the effects of additives and chopping lengths on the microbial community structure, ARGs, MGEs, and VFs during the ensiling of Sophora davidii.

Metagenomic analyses demonstrated that both additives and chopping length significantly influenced the biosafety profile of Sophora davidii silage. Additives markedly reduced the abundance of ARGs, MGEs, and VFs (P < 0.05). Formic acid (FA) demonstrated the most pronounced suppression, whereas cellulase (CE) was least effective. Notably, although inoculation with Lactiplantibacillus plantarum (LP) reduced the overall abundance of these risk factors, the strain may be associated with the vanY gene in the vanB cluster, mobile genetic elements (MGEs) such as ISLpl1 and ISLp1, as well as specific virulence factors (VFs). Furthermore, at a 5 cm chopping length, the Control group exhibited significantly higher levels of ARGs and VFs compared to the 1 cm and 3 cm treatments (P < 0.05).

The findings highlight the efficacy of reducing chopping length (to 1 cm) in controlling the proliferation and dissemination of ARGs, MGEs, and VFs. Moreover, the use of direct acidifying agents, particularly formic acid, offers considerable advantages in enhancing the microbial safety of silage.