d- and l-Aspartate regulates growth performance, inflammation and intestinal microbial community in young pigs

d-aspartate (d-Asp), an endogenous amino acid, occurs widely in animals and humans with d-enantiomers and plays an important role in the endocrine and nervous systems. However, very few studies are available on growth performance, microbial community, and the intestinal immune and inflammatory status in response to d- and l-aspartate (l-Asp). Thus, in this study, we mainly investigated the effects of dietary 1% d- and l-Asp on growth performance, inflammation, and microbial community in young pigs. Twenty-eight young pigs were randomly divided into four groups (n = 7): a control group, in which piglets were fed a basal diet, and other three groups, in which piglets received 1% d-Asp, 1% l-Asp, and 1% dl-aspartate (dl-Asp) for 35 days. The results showed that dietary 1% d-Asp significantly inhibited average daily feed intake and average daily weight gain. Gut microbes were tested and the results showed that l-Asp enhanced bacterial diversity (Shannon and Simpson). At the phylum level, l-Asp enhanced intestinal Actinobacteria and Bacteroidetes abundance but decreased Firmicutes abundance. In contrast, dl-Asp decreased intestinal Actinobacteria and Bacteroidetes abundance and increased Firmicutes abundance. At the genus level, d-Asp enhanced Clostridium sensu stricto 1 and Intestinibacter abundance. Metagenomic predictions by PICRUSt suggested that the altered microbiota were mainly involved in membrane transport, carbohydrate metabolism, amino acid metabolism, replication and repair, translation, and nucleotide metabolism. In addition, dl-Asp markedly increased the activities of serum alanine aminotransferase, aspartate transaminase and alkaline phosphatase. Also, dietary d- and dl-Asp down-regulated TLR 4, NOD1, and MyD88 in the jejunum to mediate the inflammatory response. Collectively, these results indicated that dietary d-Asp and l-Asp affect the growth performance and inflammation in piglets, which might be associated with gut microbiota.