Lawsonia intracellularis infection induces changes in microbial community function and composition associated with reduced pig growth and feed efficiency

Lawsonia intracellularis and its resulting disease remains a troubling pathogen for pork producers worldwide. In the current experiment, we aimed to characterize the microbiome of pigs challenged with L. intracellularis through peak disease impact to better understand microbial community function and how microbial changes may contribute to disease and resulting decreased growth. Twenty-four L. intracellularis negative barrows were assigned to either L. intracellularis negative (NC) or L. intracellularis challenged (PC) treatment groups (n = 12 pigs/treatment). On days post-inoculation (dpi) 0, PC pigs were inoculated with L. intracellularis. Feed disappearance was monitored daily, body weights and fecal samples were collected weekly. At dpi 21, pigs were euthanized for sample collection and macroscopic lesion scoring. Pigs challenged with L. intracellularis had sustained reductions in growth performance and feed intake throughout the 21-day period (P < 0.001). This was accompanied by changes to fecal microbial communities, particularly increased abundance of Chlamydia suis in challenged pigs at dpi 7, 14, and 21. Changes to microbial communities were also accompanied by differences in microbial metabolism, marked most notably by signatures of lesser amino acid biosynthesis and greater nucleotide synthesis in challenged pigs. In summary, L. intracellularis challenge produced reductions in growth and feed intake. This was accompanied by sustained changes to fecal microbial communities, particularly sustained increased abundance of C. suis in challenged pigs. Changes to microbial communities were also accompanied by differences in microbial metabolism which likely play a role disease.