Effects of grazing and housing system on growth performance, serum indices, rumen fermentation parameters, and microbial community in Gangba sheep.

This study investigated the effects of grazing and housing systems on growth performance, serum indices, rumen fermentation, and microbial composition of Gangba sheep in the high-altitude environment at the foot of the Himalayas. Thirty-six 4-month-old male Gangba sheep were assigned to grazing or housing systems, arranged as 9 replicates per treatment with 2 sheep per replicate, and the trial lasted 75 days (15 days of adaptation and 60 days of feeding). Compared with the grazing group, the housing system significantly increased final body weight and average daily gain (P < 0.05). Serum triglycerides, total antioxidant capacity, and glutathione peroxidase were higher, whereas total cholesterol, high-density lipoprotein cholesterol, and low-density lipoprotein cholesterol decreased (P < 0.05). Immune activation was reduced, as shown by lower immunoglobulins (IgA, IgG), interleukins (IL-2, IL-4, IL-6), tumor necrosis factor-α, and interferon-γ levels (P < 0.05), while growth hormone, growth hormone releasing hormone, and insulin-like growth factor 1 also declined (P < 0.05), indicating a nutritional feedback regulation of the growth hormone–insulin-like growth factor 1 axis. Rumen fermentation intensity increased under the housing system, with higher concentrations of ammonia nitrogen, acetate, propionate, butyrate, and total volatile fatty acids but lower pH (P < 0.05). Lipase and α-amylase activities increased, whereas cellulase activity declined (P < 0.05), suggesting a metabolic shift toward starch and lipid digestion. 16 S rRNA sequencing revealed decreased microbial α-diversity and an increased Firmicutes/Bacteroidetes ratio in the housing sheep, along with enrichment of UCG-001 and norank_o_RF39. In summary, the housing system improved growth performance, antioxidant status, and rumen fermentation efficiency while reducing immune activation and reshaping the rumen microbiota toward more energy-efficient metabolism.