Intestinal Polyamine Metabolism and Mucosal Barrier in Ningxiang and DLY Piglets: Differential Responses to ETEC Challenge

This study compared intestinal polyamine metabolism and barrier function between Ningxiang (NX) and Duroc × Landrace × Yorkshire (DLY) piglets under baseline conditions and following ETEC challenge. Experiment 1 (baseline, n = 12/breed) assessed colonic barrier integrity, immune status, polyamines, and microbiota. Experiment 2 (ETEC challenge, n = 8/group/breed) evaluated responses to oral ETEC (109 CFU) over 3 days. Under baseline conditions, NX piglets showed superior barrier integrity, higher goblet cell numbers and mucin 2 (MUC2) protein expression, and lower plasma levels of intestinal permeability markers—diamine oxidase (DAO), D-lactate (DLA), and endotoxin (ET)—compared with DLY piglets. NX piglets also exhibited reduced colonic pro-inflammatory cytokine levels (IL-6 and IL-1β) and higher expression of immune-related markers (CD3, CD68, and IgA) versus DLY piglets. In contrast, DLY piglets displayed more active microbial polyamine metabolism in the colon, with higher concentrations of putrescine, spermidine, and spermine, as well as increased ornithine decarboxylase (ODC) expression. 16S rRNA sequencing revealed greater microbial diversity and enrichment of taxa (Muribaculaceae_unclassified, Prevotella) in NX piglets, whereas DLY piglets showed enrichment of polyamine-associated genera (Collinsella, Veillonella). Following the ETEC challenge, DLY piglets displayed pronounced polyamine upregulation, including elevated polyamine levels and ODC1 expression. Conversely, NX piglets maintained more stable polyamine metabolism, higher expression of tight junction proteins (ZO-1 and occludin), lower plasma permeability markers, reduced pro-inflammatory cytokine expression (IL-6, IL-1β, IL-22), and increased anti-inflammatory IL-10 expression. Collectively, these findings demonstrate that NX piglets possess superior intestinal barrier integrity and immune maturity, while DLY piglets exhibit a more active but stress-responsive polyamine metabolic phenotype. The divergent metabolic and immune responses to ETEC challenge underscore the distinct strategies employed by these two breeds in maintaining gut homeostasis. These findings provide preliminary insights that may inform future breeding strategies aimed at enhancing intestinal health and disease resistance in pigs, pending validation in broader genetic backgrounds and mechanistic studies.