LAUSR

Subacute ruminal acidosis (SARA) is characterized by the depression of ruminal pH and an increase in the concentrations of short‐chain fatty acids (SCFAs) and lipopolysaccharide (LPS) in the rumen of cows. The onset of SARA was linked to the accumulation of SCFAs. However, the mechanism of SCFAs transport is unknown. The proton‐linked monocarboxylate transporter (MCT1) plays a vital role in the transportation of SCFAs. The goal of this study was to elucidate the distribution of MCT1 along the gastrointestinal tract of calves and adult cows; the expression change of MCT1 in SARA cows and the effect of ruminal pH, SCFAs, and LPS on MCT1 expression in rumen epithelial cells in vitro. The results indicated the presence of MCT1 along the gastrointestinal tract of calves and adult cows, most abundantly expressed in the rumen. Importantly, the expression of MCT1 was decreased in the rumen epithelium of SARA cows, and the expression of MCT1 was restored in the SARA treatment group. In vitro, LPS, low rumen fluid pH, high concentrations of SCFAs (90 mM acetate, 40 mM propionate, and 30 mM butyrate), and high concentrations of acetate, propionate, and butyrate, respectively, inhibited the expression of MCT1 in rumen epithelial cells. Taken together, these results indicated that LPS, low ruminal pH, and high concentrations of SCFAs decreased the expression of MCT1, further aggravating the accumulation of SCFAs in the rumen by decreasing the absorption of SCFAs.