Spirulina (Limnospira platensis) has gained attention as a functional feed additive in animal nutrition. However, its effects on the cecal microbiota and systemic metabolic responses in lambs remain unclear. Here, twelve 5-month-old male Hu lambs were randomly assigned to a control group (Control) or a Spirulina-supplemented group (SPI; 1.5% of dietary dry matter) and fed for 60 days (n = 6 per group). We measured serum biochemical indices, energy-metabolism variables, and immune and antioxidant parameters and characterized the cecal microbiota using 16S rRNA gene sequencing. Spirulina supplementation increased serum triglycerides (TG), glucose (GLU), alanine aminotransferase (ALT), and aspartate aminotransferase (AST) (p < 0.05). In the cecum, α-diversity indices were lower in SPI than in Control (p < 0.01), and Principal Coordinates Analysis (PCoA) indicated distinct community separation between groups (p < 0.01). Spearman correlation analyses further linked dominant genera to host metabolic and antioxidant traits. Collectively, Spirulina altered lamb metabolism and antioxidant status and reshaped the cecal microbial community, with microbial shifts associated with changes in serum indices.

Fermented total mixed ration (FTMR) is an effective approach to preserve low-quality crop residues. This study investigated the effects of ensiling duration (0, 3, 5, 7, 15 and 30 days) on nutritional dynamics, fermentation quality, in vitro digestibility, and bacterial communities of FTMR containing corn stalk and broom sorghum straw at 50% moisture. After 30 d of ensiling, FTMR had the highest crude protein content, lowest neutral detergent fiber content, peak lactic acid concentration, stable low pH, undetectable butyric acid, and maximum in vitro NDF digestibility. Bacterial alpha diversity declined significantly during ensiling, and the community was dominated by Leuconostoc, Lactiplantibacillus, and Levilactobacillus. These results clarify the microbial regulatory mechanism of mixed-straw FTMR fermentation and support the efficient utilization of crop residues in ruminant production.