Environmental Altitude and Host Genetics Shape Divergent Microbiota and a Conserved Resistome in Porcine Intestinal Niches

Environmental stressors and host genetics influence gut microbiota and antimicrobial resistance, but their combined effects across intestinal niches remain poorly unexplored. We conducted a metagenomic analysis of 60 jejunal and cecal samples from 30 native Chinese pigs across three altitudes (500 m, 1400 m, and 3850 m). The aim was to disentangle the interactive impacts of altitude, breed, and intestinal site on microbiome structure and antibiotic resistome dynamics. The cecal microbiota was taxonomically conserved and strongly associated with breed. Conversely, while jejunal communities exhibited structural variations among the sampled cohorts, differences in alpha diversity (Shannon index, p < 0.01) appeared to be primarily associated with breed differences rather than an independent altitudinal effect. High-altitude Tibetan pigs showed an enrichment of Bifidobacterium and Pseudomonas, which may be linked to hypoxia adaptation. Despite a shared core resistome (88 ARG types), the cecum harbored significantly higher ARG abundance than the jejunum within-breed comparisons of Tibetan pigs across altitudes; this revealed stable ARG profiles (p > 0.05) suggesting that, although some descriptive differences were observed, the independent effect of altitude weakens when the genetic effect is taken into account. Furthermore, carbohydrate-active enzymes (e.g., CBM13, GH33) correlated positively with ARG abundance. In conclusion, the jejunum appears to act as an environmentally responsive niche, while the cecum exhibits a higher ARG abundance that is closely associated with the host breed.