Abstract: This experiment was conducted to investigate the effects of alfalfa meal and alfalfa flavonoids on colon microflora of weaned piglets. In this experiment, 120 weaned piglets (Duroc×Landrace×Yorkshire) of similar weight and parity, and aged (35±1) days were randomly divided into 5 groups with 3 replicates per group and 8 piglets per replicate. A control group was fed a basal diet and experimental groups were supplemented with 1 (group Ⅰ), 2 (group Ⅱ), or 4 (group Ⅲ) g·kg^-1 alfalfa flavonoids and 50 (group Ⅳ) g·kg^-1 alfalfa meal per kilo added to the basal diet. A pre-experiment feed-adjustment period of 3 d was provided, and the experiment lasted for 32 days. On the final day of the experiment, colonic contents were collected. Total bacterial DNA was extracted from the colonic contents and 16S rDNA sequences were obtained using the Illumina MiSeq platform. It was found that: 1) 484 operational taxonomic units (OTUs) were detected, and 327 OTUs (67.56% of the total OTUs) belonged to five main bacterial groups. The best additive amount of OTUs was the value in treatment group Ⅰ. 2) Across treatment groups from control to Ⅳ, both ACE index and Chao index first increased, then decreased and finally increased, with group Ⅰ significantly higher (P<0.05) than the control group. Compared with the control group, Sobs, ACE and Chao indexes of group Ⅳ were not significantly different (P>0.05). The Shannon and Simpson indexes displayed no significant differences between groups (P>0.05). 3) At the phylum level, between the bacterial groups Firmicutes and Bacteroidetes, no significant differences in relative abundance were observed (P>0.05). At the genus level, relative abundance of Clostridium relative displayed a rising trend across the treatment series (P>0.05), with Clostridium relative abundance in group Ⅰ and Ⅲ, compared with the control group, significantly increased (P<0.05). Similarly, compared with the control group, relative abundance of Coprococcus 1 was significantly increased (P<0.05) in group Ⅱ, while Anaerotruncus relative abundance was significantly increased (P<0.05) in treatment groups Ⅱ and Ⅳ, and relative abundance of NC2004 was significantly increased in treatment group Ⅲ (P<0.05). UCG-014, Erysipelotrichaceae and Ruminococcaceae also displayed significant differences in relative abundance between treatment groups. It is concluded that dietary supplementation with alfalfa meal and alfalfa flavonoids can change the taxonomic composition and community structure of colonic bacteria of weaned piglets, further affecting digestion and metabolism of the nutrients.

Key words: alfalfa, alfalfa flavonoids, weaned piglets, colon, microflora