Germination-induced nutrient remodeling in wheat: linking molecular structural changes to rumen microbial community dynamics and metabolic shifts

Germination triggered by prolonged rainfall at maturity or high moisture levels during storage poses a major limitation to the use of wheat in food processing. Germinated wheat, however, represents a viable feed resource for ruminants and an opportunity for biological resource reutilization. This study systematically evaluated the effects of different germination durations on wheat nutritional composition, molecular structure, and ruminal degradability under laboratory conditions, and examined the mechanistic relationships between germination-induced molecular alterations and rumen microbial community dynamics. Prolonged germination increased dry matter loss, elevated neutral detergent fiber and crude protein, and decreased starch and non-fiber carbohydrate levels ( P < 0.050). Molecular structures analysis revealed marked alterations in protein secondary structures and carbohydrate molecular features, closely associated with nutrient remodeling ( P < 0.050). In vitro rumen fermentation showed that extended germination increased ammonia nitrogen, butyrate, the acetate-to-propionate ratio, and CH 4 production, while microbial crude protein synthesis efficiency and propionate concentration decreased ( P < 0.050). Microbial analyses further demonstrated that 24 h-germinated wheat had minimal impact on rumen microbial communities or metabolites, whereas 72 h-germinated wheat enriched fiber- associated taxon ( Rikenellaceae RC9 gut group), reduced starch-degrading bacteria ( Ruminobacter and Succiniclasticum ), and markedly downregulated the key metabolite N-acetyl-L-glutamate. In addition, integrated multi-omics analyses suggested that structural alterations in feed nutritional molecules may also be involved in shaping the characteristics of the rumen microbial community. Specifically, the relative abundances of Ruminobacter and Succiniclasticum were positively associated with TC 1 and TCA 1 , whereas Rikenellaceae RC9 gut group showed positive associations with TC 2 , TCA 2 , TCA 3 , CECH, CECA, STC 1 , STC 2 , STC 3 , and STCA. Germination markedly altered wheat nutritional and fermentative properties. Wheat germinated for 24 h can be directly included in rations, whereas wheat germinated for 72 h showed increased fiber content and enriched abundance of fiber-degrading bacteria, indicating its potential as a roughage component in ruminant diets. To ensure adequate energy supply, it should be appropriately combined with starch-rich feedstuffs to maximize nutritional value, optimize rumen fermentation and microbial activity, and enhance resource utilization efficiency.