Starter feeding altered ruminal epithelial bacterial communities and some key immune-related genes' expression before weaning in lambs

To characterize changes in ruminal epithelial bacterial communities and immune-related gene expression during concentrate starter feeding before weaning in lambs, 6 pairs of 10-d-old Hu lamb twins were selected: 1 kid received milk (M, n = 6), and the other received milk plus starter (M+ S, n = 6). All lambs received hay and water ad libitum and were slaughtered at 56-d-old. Their rumen fluid was collected to determine ruminal pH and VFA levels; rumen epithelia were collected to characterize their bacterial communities using Illumina MiSeq sequencing and to determine mRNA expression of immune-related genes using quantitative real-time PCR (qRT-PCR). Results showed that starter feeding caused a decreased ruminal pH (P = 0.004) and increased concentrations of acetate, propionate, butyrate, and total VFA (P < 0.001). Principal coordinate analysis and analysis of molecular variance revealed that starter feeding affected ruminal epithelial bacterial communities in the lambs (P = 0.001), with higher relative abundance of dominant taxa Desulfobulbus, unclassified BS11 gut group, Howardella, unclassified Synergistaceae, Bacteroides, Syntrophococcus, Pyramidobacter, Bifidobacterium, and Megasphaera (P < 0.05) but less-er relative abundance of Campylobacter, unclassified Bacteroidales, unclassified Candidate, unclassified RF9, and Snodgrassella (P < 0.05). Additionally, a phylogenetic investigation of communities by reconstruction of unobserved states analysis indicated that starter feeding markedly increased relative abundance values of dominant ruminal epithelial bacterial-inferred genes related to other ion-coupled transporters, pentose and glucuronate interconversions, glycosyltransferases, other glycan degradation, AA metabolism, sphingolipid metabolism, biotin metabolism, glycosphingolipid biosynthesis-globo series, and lysosome (P < 0.05) but decreased relative abundance values of genes related to carbon fixation pathways in prokaryotes and energy metabolism (P < 0.05) in the lambs. The qRT-PCR results showed that starter feeding decreased the relative mRNA expression of IL-6 (P = 0.003), IL-10 (P = 0.013), and interferon. (P = 0.003). Collectively, this study showed that starter feeding could alter ruminal epithelial bacterial communities and some key immune-related genes' expression in preweaned lambs. All these responses of ruminal epithelial bacteria and the immune system would be beneficial for starter-fed lambs to be weaned.