Abstract: 【Objective】The purpose of this experiment was to investigate the effects of immune stress on intestinal microflora and common bacteria changes of broiler chickens. 【Method】 One hundred and eighty 1-day old AA broilers were allocated into 4 groups. Each treatment had 5 replicate cages of 9 broilers per replicate pen. Different immune stress models, including the control group (no vaccines, NV), conventional vaccines group (CV), immune hyperthyroidism group (LPS) and immune suppression group (CYP) were set in this study. On d 21, 28, 35 and 42, each treatment group from each of 6 chickens, after slaughter, jejunum, ileum and duodenum and cecum intestinal contents were collected under sterile operation. 【Result】Gastrointestinal tract Enterobacteriaceae, Lactobacillus, Bifidobacterium and Enterococcus in broilers under immunological stress were analyzed by RT-PCR. The dynamic distribution and changes of the four bacterial species in the broiler's digestive tract were also analyzed systematically. Among the 4 genera of bacteria, changes mainly concentrated in the ileum and cecum, and the Enterobacteriaceae content was 5.03-7.88 copies/mg, Lactobacillus content was 5.48-10.34 copies/mg, Bifidobacterium content was 4.11-7.98 copies/mg, Enterococcus content was 5.61-8.79 copies/mg. The results showed that immune stress makes the four bacterial species in broiler's digestive tract change conspicuously in their genic copy when compared with CV. In which, the changes of the four bacterial species mainly represent in ileum and cecum, while the changes of days by duodenum species is not clear. 【Conclusion】 Immune stress results in the changes of the intestinal flora composition, Lactobacillus and Bifidobacterium are relatively high in NV case and LPS and CYP did not affect intestinal flora changes of chicken in late stage.

Key words: RT-PCR , intestinal microflora , immue stress , broilers