Effects Of Low Protein Diets On The Intestinal Microbiota Of Weaned Piglets And Finishing Pigs

The low protein diet could relieve the serious problems of protein source shortage and the nitrogen excretion pollution, but its effects on gut environment, especially on gut microbiota are unclear. In this paper, we mainly used the Illumina Miseq 300 sequencing platform to investigate the effects of low protein diets on microbiota of weaned piglets and finishing pigs. In Exp.1,18 weaned piglets （9.57± 0.61 kg） were randomly allotted to one of three groups. The crude protein （CP） levels in the three groups were 20%,17% and 14%, respectively. After 50 d of feeding, the content of ileum and colon were collected to analyze bacterial community structure and metabolites. Segments of ileum and colon were also collected to detect the expressions of tight junction proteins and biomarks of intestinal stem cells. The results showed that low protein diets caused a declined growth performance of weaned piglets （P< 0.05）. With the reduction of the CP level, the abundance of Weissella decreased and the abundance of potential pathogen Cyanobacteria increased. The expressions of ileal Occludin and Lgr5 were decreased （P< 0.05）. Meanwhile, with the reduction of the CP level, colonic bacterial diversity decreased, the abundance of Firmicutes increased, while the abundance of Bacteroidetes decreased. And at the family and genus level, the abundances of saccharolytic bacteria Lachnospiraceae and Lactobacillus increased, while abundance of proteolytic bacteria Phascolarctobacterium decreased with the reduction of CP level. And abundances of Ruminococcus, Prevotella, and Rikenellaceae also declined. But the expressions of colonic tight junction proteins and stem cell biomarks did not differ among three groups （P> 0.05）. As shown from the results of bacterial metabolites, intestinal concentrations of short-chain fatty acids （SCFAs） increased significantly with reduction of the dietary CP level （P< 0.05）, while the concentrations of biogenic amines decreased （P< 0.05）. In Exp.2,18 finishing pigs （62.30 ± 1.00 kg） were randomly allotted to three groups. The levels of CP in the three groups were 16%,13% and 10%, respectively. After 50 d of feeding, the samples were collected and analyzed as the same in Exp.l. The results showed that low protein diets caused a declined growth performance of finishing pigs （P< 0.05）. After CP level decreased from 16% to 10%, ileal and colonic bacterial diversity decreased. As for ileal bacterial community, abundance of Clostridium_sensu_stricto₁ decreased, while the abundance of Escherichia-Shigella increased. The expressions of ileal Lgr5 and Bmil significantly decreased （P< 0.05）. As for colonic bacterial community, the abundance of Firmicutes increased, with Bacteroidetes decreased. At the family and genus levels, the abundance of saccharolytic bacteria Lachnospiraceae increased, while abundance of proteolytic bacteria Phascolarctobacterium decreased with the reduction of dietary CP level. And abundances of Rikenellaceae, Prevotella and Ruminococcus also declined. But expressions of colonic tight junction proteins and stem cell biomarks did not differ among three groups （P> 0.05）. However, when the dietary CP level decreased to 13%, abundance of Lactobacillus in ileal content increased, and expressions of ileal Occludin and Claudin-1 increased. And abundance of Megasphaera, the genus of Veillonellaceae was much greater in colonic content of 17% CP group than in the other two groups. As shown from the results of bacterial metabolites, intestinal concentrations of SCFAs and biogenic amines decreased with the reduction of dietary CP level （P< 0.05）. In conclusion, dietary CP level reduction may violate the ileal barrier function and proliferation of ileal stem cell of weaned piglets by promoting the pathogen in ileum, but a moderate reduction of dietary CP level may have beneficial effects on the ileal microflora and barrier function of finishing pigs. Dietary CP level also altered the colonic bacterial community structure, but had slight effects on colonic barrier function and stem cell proliferation.