Weaning age impacts intestinal stabilization of jejunal intraepithelial T lymphocytes and mucosal microbiota in pigs

Weaning in conventional pig production is a stressful event that involves abrupt dietary and environmental changes, and the post-weaning period is associated with increased incidence of disease and antibiotic use. As a result, there is a growing demand for non-antibiotic practices to enhance health during this phase of production. Current production systems wean piglets at a relatively young age, and it is unclear if age at weaning impacts shifts in intestinal immune populations, particularly intraepithelial T lymphocyte (T-IEL) populations, or bacterial communities in a comparable timeframe and magnitude. T-IELs reside in the intestinal epithelium and play a role in intestinal integrity and defense. While later weaning may be an approach to minimize the negative impacts of weaning, the impact of age at weaning on T-IEL abundances and function is not clearly understood. Our results indicate pigs weaned at 18–21 days of age (standard weaned, SW), which is consistent with production practices in the United States, had delayed shifts in T-IEL populations when compared to pigs weaned at 25–28 days of age (late weaned, LW), which is consistent with practices in the European Union. Specifically, the abundance of induced T-IELs (CD8ab ⁺ ab T cells) in the jejunum increased between 0 and 3 days post weaning (dpw) for the LW group and stabilized, but shifts were delayed until between 3dpw and 7dpw in the SW group. Concomitant decreases in the abundance of natural T-IEL (gd T cells) were detected. The structure of jejunal mucosal bacterial communities were comparable between SW and LW pigs at 0dpw, but the SW group had more pronounced shifts from 3dpw to 7dpw and 7dpw to 14dpw compared to minimal shift in LW group from 7dpw to 14dpw. Body weight between groups was comparable when adjusted for age. Overall, the bacterial communities of the jejunal mucosa were more stable after weaning in LW than SW pigs, and jejunal T-IEL abundances stabilized more rapidly in the LW group. As T-IELs play a key role in intestinal homeostasis and barrier integrity, the early differences in population abundance may be indicative of functional differences as well.