Abstract: 【Objective】 The experiment aimed to analyze the differences in the composition and abundance of intestinal microbiota in piglets with different birth weights during the lactation period,identify the key microbiota markers that affect subsequent development,and provide a scientific basis for the formulation of piglet health care strategies. 【Method】 Ten second-time pregnant sows with similar body conditions were selected and fed uniformly.After the piglets were born,one low birth weight piglet and one normal birth weight piglet were selected in each litter according to their body weight to form a normal birth weight piglet group (NBWP,1.58 kg±0.04 kg) and a low birth weight piglet group (LBWP,0.98 kg±0.02 kg),with 10 piglets in each group and half males and half females. Fecal samples were collected from piglets in each group at 3,7,14 and 21 days old.DNA was extracted,quality-filtered,and clustered into OTUs.Species composition was analyzed through database comparison,and Alpha and Beta diversity were calculated using QIIME2.PL-DA analysis was performed using the R language mixOmics package. 【Result】 At the ages of 3,7,14 and 21 days,the body weight of piglets in NBWP group was extremely significantly higher than that in LBWP group (P＜0.01).NBWP group obtained 2 478 OTUs,and LBWP group obtained 1 721 OTUs.The changing trends of Alpha diversity and Beta diversity in the two groups at the same age were similar,but the microbiota diversity and abundance in LBWP group were significantly lower than those in NBWP group.The dominant bacterial phyla in the intestines of the two groups of piglets were all Firmicutes,Bacteroidetes and Proteobacteria.At 3 days of age,the relative abundance of Firmicutes in the intestinal tract of piglets in LBWP group was significantly higher than that in NBWP group,and the relative abundance of Proteobacteria was significantly lower than that in NBWP group.Bacteroides, Lactobacillus and Prevotella were the dominant bacterial genera in the intestines of piglets in the two groups.The relative abundance of Bacteroides in the intestines of piglets in LBWP group was higher than that in NBWP group and the relative abundance of Lactobacillus was lower than that of NBWP group.Further studies havd found that the weight differences between piglets in LBWP and NBWP groups were closely related to the abundance changes of Bacteroidetes,Firmicutes and other bacteria. 【Conclusion】 The difference in the birth weight of piglets had an impact on the early colonization process of intestinal microorganisms,and thereby affected the growth and development process of piglets.This study explored the differences in intestinal microbiota among piglets with different birth weights,which could provide a reference for subsequent regulation of intestinal microbiota to improve the growth and development status of piglets.

Key words: piglets; birth weight; feeding period; microbial diversity; dominant genus