Insight into the long-term impact of birth weight on intestinal development, microbial settlement, and the metabolism of weaned piglets

Infant mortality of low birth body weight (LBBW) piglets can reach 10% and is mainly due to gut and immune system immaturity which can lead to a higher risk in the long term. This study aimed to assess the impact of birth body weight (BBW) on piglet metabolism, gut status, and microbial profile from weaning to 21 d postweaning. At birth, 32 piglets were selected for their BBW and inserted into the normal BBW (NBBW:1.38 +/- 0.09 g) or the LBBW (0.92 +/- 0.07 g) group. The piglets were weighed weekly from weaning (d0) to d21. At d9 and d21, 8 piglets/group were slaughtered to obtain the distal jejunum for morphology, immunohistochemistry, and gene expression analysis, colon content for microbiota and short-chain fatty acid (SCFA) analysis, and intestinal content for pH measurement. Blood was collected for metabolomic, haptoglobin (Hp), and reactive oxygen metabolite (ROM) analysis. The LBBW group had a lower body weight (BW) throughout the study (P < 0.01), a lower average daily gain from d9-d21 (P = 0.002), and lower feed intake (P = 0.02). The LBBW piglets had lower Hp at d9 (P = 0.03), higher ROMs at d21 (P = 0.06), and a net alteration of the amino acid (AA) metabolism at d9 and d21. A higher expression of NFKB2 was observed in the LBBW piglets at d9 (P = 0.003) and d21 (P < 0.001). MYD88 expression was enhanced in NBBW piglets at d9 (P < 0.001). The LBBW piglets had a lower villus height, absorptive mucosal surface (P = 0.01), and villus height:crypt depth ratio (P = 0.02), and a greater number of T-lymphocytes in both the epithelium and the crypts (P < 0.001) at d21. At d21, the LBBW piglets had higher lactic acid, acetate, butyrate, and valerate, and also higher SCFA in the colon (P < 0.05). The LBBW piglets had a higher Shannon index (P = 0.01) at d9 and a higher abundance of SCFA-fermenting bacteria. In conclusion, the present study confirmed that LBBW could impact the gut mucosal structure, immunity, and inflammatory and oxidative status, leading to an altered AA metabolism, and delaying the recovery from weaning.