Weaning of piglets is generally considered as a stressor which changes intestinal ecosystem and leads to clinical implications. Microbiota inhabiting in small intestine （especially ileum） are assumed to promote health, but their functional properties are yet poody dascdbed. As indicated by the 16S rRNA gene sequences of ileal micrebiota in nursing piglets （at the age of 21 and 28 d） and 28-day-old weaned piglets （weaned at 21 d of age）, the microbiota were mainly comprised of gram-positive bacteria. There were 40 operational taxonomic units （OTUs） （from 171 clones） in the ileum of nursing piglets aged 21 d, 61 OTUs （from 194 clones） in the ileum of nursing piglets aged 28 d, and 56 OTUs （from 171 clones） in the ileum of weaned piglets aged 28 d. The flea of nursing piglets aged 21 d were dominantly occupied by Lactobacilli （87.7%） as well as Streptococ cus （ 3.5 % ）. Lactobacillus amy/ovorus （41.5 % ）, Lactobaci/lus sp. （ 19.3 % ）, Lactobaci/lus reuteri （ 12.3 % ）, Lactobacillus salivarius （ 9.4 % ） and L. mucosae （4.7%） were the predominant species among Lactobacil/L Similar results were obtained in the nursing piglets at 28 d of age ex- cept that Lactobaci/li decreased to 71.1% and Streptococcus increased to 21.1% significantly. Lactobacillus （52.0%） and Streptococcus （26.3%） were the two major groups in the ileum of weaned piglets aged 28 d. Lactobacillus amylovorus （31.6%） and Lactobaci/lus reuteri （ 16.4% ） was the two most important species in Lactobacillus. Therefore, Lactobacilli were predominant in the ileum of nursing and weaned piglets, and they had the highest diversity, followed by Streptococcus. The diversity of ileal microbiota was not different remarkably between the nursing piglets and the weaned piglets, but the composition changed significantly. These findings are helpful to understand ileal bacterial ecophysiology and further develop nutritional regimes to prevent or counteract complications during the weaning transition.
