Dietary modulation of the expression of genes involved in short-chain fatty acid absorption in the rumen epithelium is related to short-chain fatty acid concentration and pH in the rumen of goats.

We have tested the hypothesis that increased concentrate intake induces mRNA abundance alterations of genes involved in short-chain fatty acid (SCFA) absorption in the rumen epithelium of goats and these changes of mRNA abundance are probably related to ruminal SCFA concentration and ruminal pH. Goats (n=12) were randomly allocated to 2 groups and fed either a low-concentrate (LC) diet (10% concentrate; n=6) or a medium-concentrate (MC) diet (35% concentrate; n=6) in 2 equal portions daily. Goats were fed separately with their respective diet for 3 wk. The goats were slaughtered 6h after the morning feeding on d 22. In vivo, goats in the MC treatment exhibited a greater ruminal SCFA concentration (81.9mM) compared with those in the LC treatment (58.0mM), and the pH decreased from 7.03 to 6.63. Correspondingly, mRNA expression of candidates for SCFA(-)/HCO3(-) exchangers, namely downregulated in adenoma (DRA), putative anion transporter 1 (PAT1), and anion exchanger 2 (AE2) were increased in the MC group. Further, upregulation in monocarboxylate transporter 1 (MCT1) and monocarboxylate transporter 4 (MCT4) mRNA abundances was observed in the MC group. The expression of genes that help the rumen epithelial cells to maintain intracellular pH, including Na(+)/H(+) exchanger 1 (NHE1), NHE2, NHE3, vacuolar H(+) ATPase subunit B (vH(+)ATPase), and Na(+)/K(+) ATPase pump subunit α1 (Na(+)/K(+)ATPase) were also enhanced in the MC group relative to the LC group. During in vitro studies with isolated rumen epithelial cells from goats, exposure to a pH of 6.8 increased MCT1 mRNA expression after 24h of culture, whereas the mRNA expression of AE2 was downregulated. The presence of SCFA (20mM) in the medium increased DRA, PAT1, AE2, MCT1, and Na(+)/K(+)ATPase mRNA expression. The expression of vH(+)ATPase was decreased by increased SCFA concentration. The mRNA expression of MCT4 did not vary in vitro with pH (6.8) or SCFA (20mM). The expression of DRA was increased by synergistic effects of higher SCFA concentration and lower pH, similar to that of MCT1. Thus, diet-dependent rumen epithelial mRNA expression changes in genes involved in SCFA absorption are probably related to ruminal SCFA concentration and pH.