试验第8～14d仔猪日增重和肉料比随VA添加水平的升高而线性提高（P=0.02、P=0.005）。16mg/kg VA组空肠Lgr5+基因表达显著提高（P=0.012）。4 mg/kg VA组的空肠绒毛高度和绒毛表面积显著提高（P值分别为0.027和0.035）。4、8mg/kg VA组隐窝深度显著增加（二次方程式，P=0.043），16mg/kg VA组绒毛高度：隐窝深度显著提高（二次方程式，P=0.015）。当进一步补充4mg/kg VA时，麦芽糖酶、蔗糖酶和碱性磷酸酶活性显著提高（P=0.032、0.041、0.024）。2mg/kg VA组的Slc2a2 mRNA丰度显著提高（线性，P=0.024）。此外，VA及其代谢产物（视黄酸）显着降低了仔猪肠道类器官的出芽率，每个类器官的出芽数以及嗜铬粒蛋白A和Muc2的表达（P <0.05）。与对照组相比，Spp1和Trop2的表达显著提高。
Dietary vitamin A affects growth performance, intestinal development, and functions in weaned piglets by affecting intestinal stem cells
Vitamin A (VA) is an important nutrient for weaning piglets. It plays a significant role in the normal formation, development, and maintenance of epithelial cells. Previous studies have shown that VA supplements could improve the host’s intestinal barrier function. Therefore, we hypothesized that VA supplements can affect intestinal function in weaned piglets by regulating intestinal stem cells. Thirty-two 21-d-old weaned [(Yorkshire × Landrace) × Duroc] piglets with an average weight of 8.34 ± 0.13 kg were randomly divided into 4 treatment groups, with 1) 2 mg/kg (control), 2) 4 mg/kg, 3) 8 mg/kg, and 4) 16 mg/kg doses of VA, respectively. The experiment lasted for 14 d. Weaned piglets were given ad libitum access to food and water during the test. The ADG (linear, P = 0.020) and G:F (linear, P = 0.005) of the piglets were found to increase significantly from days 8 to 14. The Lgr5+ gene expression (P = 0.012) in the jejunum mucosa of the 16 mg/kg VA group was increased. The jejunum villus height (P = 0.027) and villi surface area (P = 0.035) were significantly increased in the 4 mg/kg VA treatment group. The crypt depth increased significantly in the 4 and 8 mg/kg VA treatment groups (quadratic, P = 0.043), and the ratios of villus height to crypt depth significantly increased in the 16 mg/kg VA group (quadratic, P = 0.015). The maltase (P = 0.032), sucrose (P = 0.041), and alkaline phosphatase activity (linear, P = 0.024) were significantly increased when further supplemented with 4 mg/kg VA. Slc2a2 mRNA abundance was significantly increased in the 2 mg/kg VA group (linear, P = 0.024). Moreover, the budding rates, buddings number per organoid, and Chromogranin A and Muc2 expression of piglet intestinal organoids were significantly reduced (P < 0.05) by VA and its metabolites (retinoic acid). Compared with the control group, the expression of Spp1 and Trop2 increased. These results indicated that VA may increase the stemness of intestinal stem cell in vitro. This study suggested that VA could affect growth performance and intestinal function by regulating intestinal stem cells in the jejunum of weaned piglets.