The impact of adding selenium-enriched spirulina platensis on the quality and microbial community of alfalfa silage

To improve the quality and extend the preservation of forage, natural functional additives are increasingly explored for silage preparation. This study aims to investigate the effects of Selenium-enriched Spirulina platensis (Se-Spirulina) as a functional additive on the nutritional quality, fermentation characteristics, and microbial community of alfalfa silage. Four treatments were established: a control and treatments supplemented with 1%, 3% and 5% Se-Spirulina, designated CK, FXZ1, FXZ3 and FXZ5, respectively. After 60 days of ensiling, a systematic analysis was conducted on the nutritional components, fermentation quality, and bacterial community structure. The results showed that the addition of Se-Spirulina significantly increased the dry matter(DM) and crude protein(CP) content, reduced the neutral detergent fiber(NDF) and acid detergent fiber(ADF) levels, with the 5% addition showing the optimal effect. Se-Spirulina promoted lactic acid(LA) accumulation, accelerated pH decline, and significantly inhibited the production of propionic acid (PA), butyric acid (BA), and ammonia nitrogen(NH3-N). Microbial analysis revealed that Se-Spirulina enhanced the abundance of dominant LAB such as Lactiplantibacillus and inhibited the growth of potential spoilage bacteria. Functional prediction results indicated that it could enhance the activity of the silage microbial community in pathways such as carbohydrate and amino acid metabolism, improving the fermentation microenvironment. In summary, Se-Spirulina is a highly effective natural additive that combines nutritional regulation with fermentation optimization, demonstrating promising application prospects.