Artemisia argyi Polysaccharides Protect Intestinal Health by Enhancing Antioxidant Capacity in Suckling Lambs Under Cold Exposure

Cold exposure severely impairs intestinal homeostasis and growth in young lambs. This study investigated the protective effects of Artemisia argyi polysaccharides (AAPs) on intestinal health in cold-exposed suckling lambs. Twenty-four 7-day-old lambs were randomly allocated to receive a milk replacer supplemented with 0 (Control, C), 0.5 (Low-dose, LA), 1.0 (Medium-dose, MA), or 2.0 g/kg (High-dose, HA) of AAPs for 14 days under cold conditions (−8 °C to −5 °C). The results showed that the MA group significantly increased ADG and decreased the F/G (p < 0.05) compared to the control. Both LA and MA groups significantly improved EE and Ca digestibility, while the MA group further increased CP and P digestibility (p < 0.05). The LA group enhanced jejunal chymotrypsin and lipase activities, whereas the MA group elevated chymotrypsin, lipase, and α-amylase activities (p < 0.05). Additionally, both LA and MA upregulated Nrf2 mRNA expression (and downregulated Keap1 mRNA expression in the jejunum), suggesting activation of the Nrf2/Keap1 pathway; the MA group significantly upregulated CAT, GSH-Px, and SOD1 mRNA expressions, enhanced SOD and CAT activities, and reduced colonic MDA content (p < 0.05). The MA group also significantly elevated the VH/CD across the small intestine, upregulated tight junction genes (Claudin-1 and Claudin-4 in jejunum; ZO-1 and Claudin-1 in colon), and decreased serum D-LA and DAO levels (p < 0.05). Cecal microbiota sequencing showed that AAPs enriched the relative abundance of Anaerofilum and reduced Akkermansia. In conclusion, 1.0 g/kg AAP supplementation effectively mitigates intestinal oxidative stress, improves barrier integrity, and modulates gut microbiota, thereby enhancing nutrient digestibility and growth performance in cold-stressed suckling lambs.