Alpha diversity of the cecal microbiome of poults at 2 d (A) and 7 d (B) after inoculation represented as Shannon diversity index. From the day of hatch, the poults were allocated into N, P, and S groups for 14 d; a indicates P > 0.05. Abbreviations: N, Negative control (poults without SH challenge or PF supplementation); P, test group (poults supplemented with PF for 14 d and challenged with SH on d 7); PF, Propionibacterium freudenreichii; S, SH control (poults challenged with SH on d 7 and without PF supplementation); S, SH control (poults challenged with SH on d 7 and without PF supplementation)SH, Salmonella Heidelberg.