Differential Regulation of Ruminal Microbial Community Structure and Functional Pathways in Sheep Supplemented with Linseed Oil or Sunflower Oil

This study evaluated the effects of dietary PUFA supplementation on growth performance, serum biochemical indices, rumen morphology, ruminal fermentation, and rumen microbial communities in Hu sheep. Thirty healthy male Hu sheep (80 days old; 18.70 ± 0.72 kg) were randomly assigned to three groups (n = 10/group) and fed a basal diet supplemented with 4% rumen-bypass palmitic acid fat powder (POS), 4% linseed oil (LO; rich in ω-3 PUFA), or 4% sunflower oil (SO; rich in ω-6 PUFA). PUFA supplementation did not affect average daily gain or rumen tissue morphology (p > 0.05), but it significantly reduced serum creatinine, uric acid, and high-density lipoprotein concentrations (p < 0.05). Orthogonal comparative analysis showed that supplementing with PUFA significantly reduced acetate and propionate, while increasing isobutyrate, butyrate, isovalerate, and TVFAs (p < 0.05). The levels of propionate, butyrate and TVFAs in the SO group were higher than those in the LO group (p < 0.05), and the ratio of acetate to propionate was lower (p < 0.05). Supplementing with PUFA reshaped the rumen microbiota, increasing the relative abundances of Bacteroidota, Firmicutes, Euryarchaeota, Cyanobacteria, and Actinobacteriota, while decreasing Proteobacteria and Desulfobacterota (p < 0.05). At the genus level, Prevotella and Rikenellaceae_RC9_gut_group were enriched in both groups with added PUFA, while Prevotellace-UCG-001 was specifically enriched in the LO group; in contrast, Prevotella_7, Succinivibriaceae_UCG-001, Prevotella_9, and Dialist all showed a decrease (p < 0.05). The alpha diversity increased, while the beta diversity showed significant differences between the group with added PUFA and the control group. Functionally, LO enriches carbohydrate and energy metabolism, while SO enriches nucleotide metabolism. In summary, linseed oil and sunflower oil improved serum indices and ruminal fermentation without impairing growth, but through distinct microbial and functional pathways.