Effects of dietary indole-3-acetate sodium on intestinal morphology, nutrient absorption, and inflammatory responses in weaned piglets

Weaning stress can severely damage the piglets' intestines. Microbial tryptophan catabolites play a vital role in maintaining the health of the intestinal mucosa. Indole-3-acetic acid (IAA), an indole derivative with known anti-inflammatory properties, has not yet been studied for its impact on piglets' intestinal health. Twenty-four weaned crossbred piglets (Duroc × Yorkshire × Landrace, weighing 6.58 ± 0.07 kg) were randomly allocated to receive diets containing 0, 120, or 240 mg/kg indole-3-acetate sodium (IAA-Na). Although dietary IAA-Na did not significantly impact growth performance or diarrhea incidence (P > 0.05), the 240 mg/kg IAA-Na elevated jejunal villus width (P < 0.05), tended to increase villus surface area (P < 0.10), and enhanced apparent nutrient digestibility alongside upregulating the mRNA expression of transporters (P < 0.05). Furthermore, dietary IAA-Na promoted intestinal epithelial cell proliferation and reduced secretory cell numbers (P < 0.05). Transcriptomic analysis of the jejunum of the 240 mg/kg group revealed significant modulation of pathways related to the "inflammatory response" and "immune system processes." Consistent with this, dietary supplementation with 240 mg/kg IAA-Na downregulated the content and expression of proinflammatory cytokines while upregulating the content and expression of anti-inflammatory cytokines in the jejunum. To further elucidate the effect of IAA on epithelial renewal, piglet jejunal organoids were employed as an in vitro model. Treatment with 0.5 and 2 μM IAA-Na significantly increased the organoids budding rate on d 3 (P < 0.01), indicating enhanced epithelial renewal capacity. In conclusion, although dietary IAA did not improve overall growth performance, 240 mg/kg IAA-Na promoted nutrient absorption in weaned piglets, potentially through enhancing anti-inflammatory responses and epithelial renewal.