Restored intestinal integrity, nutrients transporters, energy metabolism, antioxidative capacity and decreased harmful microbiota were associated with IUGR piglet's catch-up growth before weanling

Intrauterine growth restriction (IUGR) is a major inducer of higher morbidity and mortality in the pig industry and catch-up growth (CUG) before weanling could significantly restore this negative influence. But there was limited knowledge about the underlying mechanism of CUG occurrence.Eighty litters of newborn piglets were divided into normal birth weight (NBW) and IUGR groups according to birth weight. At 26 d, those piglets with IUGR but over average body weight of eighty litters of weaned piglets were considered as CUG, and the piglets with IUGR still below average body weight were considered as NCUG. This study was conducted to systemically compare the intestinal difference among NBW, CUG and NCUG weaned piglets considering the crucial role of the intestine for piglet growth.The results indicated that the mRNA expression of nutrients (amino acids, glucose, and fatty acids) transporters, and mitochondrial electron transport chain (ETC) I were upregulated in CUG piglets' gut with improved morphology compared with those NCUG, as well as the ratio of P-AMPK/AMPK protein expression which is the indicator of energy metabolism. Meanwhile, CUG piglet's gut showed higher antioxidative capacity with increased SOD and GSH-Px activity, decreased MDA levels, as well as higher mRNA expressions of Nrf2, Keap1, SOD, and GSH-Px. Furthermore, inflammatory parameters including TNF-α, IL-1β, IL-6, and IL-12 factors, and the activation of MAPK and NF-κB signaling pathways were significantly elevated in the NCUG intestine, while the protein expression of ZO-1, Occludin and Claudin-1 was reduced. The alpha diversity of fecal microbiota was higher in CUG piglets in contrast with NCUG piglets, and the increased beneficial bacteria and decreased pathogenic bacteria was also observed in CUG piglets.CUG piglet's intestine showed comprehensive restoration including higher nutrients transport, energy metabolism, antioxidant capacity, and intestinal physical barrier, while lower oxidative stress, inflammatory response, and pathogenic microbiota.