Probiotic–Enzyme Synergy Regulates Fermentation of Distiller’s Grains by Modifying Microbiome Structures and Symbiotic Relationships

The high fiber content and low rumen digestibility prevent the efficient use of distiller's grains (DGS) in ruminant feeds. This study investigated the effects of probiotics (<i>Lactiplantibacillus plantarum</i> and <i>Bacillus subtilis</i>) and enzymes (β-glucanase, xylanase, β-mannanase, and cellulase) on DGS nutrient content, ruminal degradability, and microbial communities under anaerobic storage for 30 days. Groups included control (C), probiotics (B), enzymes (E), and their mixture (EB). As compared to groups C, B, and E, neutral detergent fiber (NDF), acid detergent fiber (ADF), hemicellulose, and cellulose contents were significantly decreased and the ruminal degradability of NDF and ADF at 48 h was significantly increased in group EB (<i>p</i> < 0.05). Enzyme activities significantly affected bacterial abundance, and the contents of these enzymes were negatively correlated with the content of fibrous components. The abundances of <i>Bacillus</i> and <i>Rummeliibacillus</i> were negatively correlated with fiber content but positively correlated with the activities of these enzymes. The symbiotic relationship between <i>Bacillus</i> and <i>Anaerocolumna</i> in the EB group sustained the synergistic effects of probiotics and enzymes. Co-fermentation of probiotics and enzyme additives enhanced the nutritional value of DGS, which was associated not only with probiotic-enzyme synergy but also variations in dominant microbes and microbiome commensal relationships.