Effects of Sea Buckthorn Flavonoids on Growth Performance, Blood Biochemical Indexes, Rumen Fermentation and Rumen Bacteria of Hu Sheep Fed with High-Concentrate Diet

This study evaluated the effects of dietary sea buckthorn flavonoid (SF) supplementation on growth performance, serum biochemical, antioxidant, and immune indices, rumen fermentation, and ruminal bacterial composition in Hu sheep fed a high-concentrate diet. Thirty 6-month-old fattening Hu sheep were randomly assigned to a high-concentrate control diet (HC) or the same diet supplemented with 0.30% SF (HT; n = 15 per group) for 45 days. Compared with the HC group, SF supplementation increased average daily gain (p = 0.04) and reduced the feed conversion ratio (p = 0.01) without affecting average daily feed intake. Serum total protein, alanine aminotransferase, total antioxidant capacity, IgA, IgG, IL-2, IL-8, and IL-1β were increased in the HT group (p ≤ 0.05). Ruminal acetate and valerate concentrations increased (p = 0.01 and p = 0.03, respectively), and total volatile fatty acid concentration showed an increasing tendency (p = 0.06), whereas rumen pH was unaffected. The relative abundances of Succiniclasticum and Acidaminococcus increased in the HT group (p < 0.05), indicating modulation of specific ruminal bacterial taxa. In conclusion, supplementation with 0.30% SF improved growth efficiency, antioxidant status, selected immune indices, and specific rumen fermentation and bacterial responses in Hu sheep fed a high-concentrate diet. However, the isolated increase in serum alanine aminotransferase may indicate hepatic metabolic adaptation or mild liver stress. Dose–response and time-course studies incorporating liver-specific biomarkers and histopathological evaluation are required to clarify the hepatic safety of sea buckthorn flavonoid supplementation.