Inappropriate microbial colonization can induce gastrointestinal ( GI) inflammation may predispose poultry to opportunistic infections and reduce growth performance. Four independent experiments were completed to test ability of select Enterobacteriaceae isolates to induce GI inflammation. Experiments 1 and 2 included a non-inoculated control ( NC), and a low ( L), medium ( M), or high ( H) day of hatch ( DOH) oral inoculation level. In experiment 1, birds in L1, M1, and H1 received 10 2 to 10 4 CFU of a mixed dose of 2 species of Citrobacter and Salmonella Enteritidis LB (SE). In experiment 2, birds in L2, M2, and H2 received 10 3 to 10 5 CFU of E. coli LG (LG) and included NC. Body weight was recorded on d 0, 7, and 14, with blood collected for chicken serum alpha-1-acid glycoprotein ( A1GP) measurements on d14. Neither experiment resulted in differences in BWG, however, A1GP was increased ( P < 0.05) on d 14 when DOH inoculation dose 10 3 CFU/chick was used compared to NC. This observed increase in A1GP resulted in selection of 10 3 CFU/chick for DOH inoculation in experiments 3 and 4. Experiment 3 consisted of NC, E. coli Huff (Huff), and SE. On d 0, 7 and 15, BW was measured, with blood collected on d 15 for A1GP. Both d 15 A1GP and BWG from d 7 to 15 were reduced in inoculated chicks, Huff and SE, in experiment 3 ( P < 0.05). Experiment 4 evaluated NC and LG with BW measured on d 0, 2, 7 and 14. Yolk sacs were evaluated for retention and bacterial enumeration, and blood for serum A1GP were collected on d 2 and 14. Experiment 4 resulted in no differences in yolk sac parameters or A1GP, whereas there was an increase in BWG for LG from d 0 to 14 ( P < 0.05). When evaluated over time, serum A1GP increased between d 2 and d 14 by nearly 46% in LG, compared to negligible changes in NC ( P = 0.111). Mild GI inflammation induced by early Enterobacteriaceae exposure may not drastically impact growth or inflammation parameters but may increase susceptibility to opportunistic infection necessitating further study of this model.