Dietary Supplementation With Mannitol Regulates the Rumen and Intestinal Microbiome, Immune Function, and Antioxidant Capacity of Grazed Mongolian Sheep

This study aimed to investigate the short-term effects of mannitol supplementation on grazing Mongolian sheep, including ruminal and intestinal microbiome, serum biochemical parameters, and immune and antioxidant functions. Ten sheep were randomly divided into control and experimental groups (n = 5) receiving without or with 10 g/kg mannitol, respectively. After 20 days, including a 5-day adaptation, mannitol did not affect the average daily gain and rumen fermentation but significantly altered microbial composition, as evidenced by principal coordinates' analysis. The abundances of genera including Rikenellaceae_RC9_gut_group increased notably in the rumen, and those of Alistipes and Norank_f_Muribaculaceae increased in intestine with mannitol supplementation. Mannitol increased the serum concentrations of total protein, albumin, retinol-binding protein, paraoxonase, and total cholesterol and decreased alanine aminotransferase levels. Mannitol also increased the levels of immunoglobulins, interleukins, tumor necrosis factor, interferon, and complements and antioxidant enzyme activities while reducing malondialdehyde and hydrogen peroxide concentrations. The serum total protein positively correlated with Rikenellaceae_RC9_gut_group and Alistipes while negatively correlated with superoxide dismutase and specific microbial genera. Taken together, mannitol supplementation reshapes ruminal and intestinal microbial communities, improving serum biomarkers, immune responses, and antioxidant defenses in grazing Mongolian sheep. These findings offer insights into novel feeding strategies for the management of grazing sheep.