Artemisia annua Residue Regulates Immunity, Antioxidant Ability, Intestinal Barrier Function, and Microbial Structure in Weaned Piglets

<i>Artemisia annua</i> residue (AR), as the byproduct of industrial extraction of artemisinin, contains rich nutrients and active ingredients. This study was conducted to determine the effects of AR as an unconventional feed material on growth performance, immunity, and intestinal health in weaned piglets. Thirty-two piglets weaned at 21 days (7.53 ± 0.31 kg average BW) were fed with a corn-soybean basal diet (BD) and a basal diet with 1% (LAR), 2% (MAR), and 4% (HAR) AR diets for 28 days. AR diets increased the serum IgA and complement component 3 levels, superoxide dismutase activity, and villus height in the duodenum (<i>p</i> < 0.05). The MAR group increased the ADG, serum total protein, and mRNA expression levels of Claudin-1 in the duodenum and zonula occludens-1 (ZO-1) and the mucin 2 (MUC2) in the colon, as well as colonic <i>Romboutsia</i> and <i>Anaerostipes</i> abundances, and decreased the <i>Proteobacteria</i> abundance (<i>p</i> < 0.05). To sum up, dietary AR supplementation may enhance growth performance by improving serum immunoglobulin and antioxidant enzyme activity, intestinal morphology, tight junction protein expression, and gut microbiota of weaned piglets. Regression analysis showed that the optimal AR supplemental level for growth performance, immunity, antioxidant ability, and intestinal health of weaned piglets was 2.08% to 4.24%.