Sheep-derived probiotics alleviate weaning-induced oxidative stress in lambs via the gut-liver axis

Weaning is a critical transition in lamb production that can disrupt intestinal homeostasis, promote oxidative stress, and contribute to liver injury. This study investigated whether sheep-derived probiotics could mitigate weaning-associated hepatic injury through the gut-liver axis. Microbiota profiling of six intestinal segments from healthy Hu sheep led to the isolation of nine lactic acid bacterial strains. After in vitro screening for antimicrobial and antioxidant activities, Lactiplantibacillus plantarum M1 and Limosilactobacillus reuteri K4 were selected and administered daily to early-weaned lambs from birth to day 30. Probiotic supplementation partially restored relative organ weights, alleviated hepatic histopathological damage, and reduced biochemical markers of liver injury. It also modulated the colonic mucosal microbiota, enhanced intestinal barrier integrity, and increased colonic acetate and butyrate levels. Liver metabolomics revealed enrichment of the pentose phosphate pathway and glutathione metabolism, accompanied by increased hepatic spermidine abundance and activation of the Nrf2-Keap1 antioxidant pathway. Cell-based validation further showed that spermidine attenuated oxidative stress, at least in part, through modulation of Nrf2-Keap1 signaling. Together, these findings suggest that sheep-derived probiotics may alleviate weaning-induced liver injury in lambs through coordinated microbial, metabolic, and antioxidant regulation along the gut-liver axis.