Butyrate and Subacute Ruminal Acidosis Affect Abundance of Membrane Proteins Involved with Proton and Short Chain Fatty Acid Transport in the Rumen Epithelium of Dairy Cows

The objective of this study was to elucidate the effects of butyrate on the Short Chain Fatty Acids (SCFA) membrane transport proteins and proton membrane transport proteins in the rumen epithelium. Sixteen mid-lactation cows were fed a 44% Non-Fibre Carbohydrate (NFC) diet and divided into a control treatment and a butyrate treatment. For 7 days, the cows on the control treatment received a carrier treatment and the cows on the butyrate treatment received a ruminal butyrate dose at the rate of 2.5% of Dry Matter Intake (DMI). Rumen pH was measured on days 6 and 7 and rumen biopsies were taken on days 1 and 7. Rumen pH measurements confirmed the occurrence of ruminal acidosis in both treatment groups, defined as a rumen pH of 5.6 for at least 3 h per day. Between the control and butyrate treatment, there was no difference in rumen pH profile. Immunofluorescence analysis performed on longitudinal ruminal papillae cross-sections showed that for the duration of the study, protein abundance in the stratum basale increased for Monocarboxylate Cotransporter Isoform 1 (MCT1), sodium/proton exchanger isoform 3 (NHE3) and sodium/Bicarbonate Cotransporter Isoform 1 (NBC1). There was a time*treatment interaction for MCT1 and NBC1, with the butyrate treatment group showing a higher abundance of MCT1 and a lower abundance of NBC1 at day 7. Luminal butyrate appears to increase SCFA uptake capacity by increasing the abundance of MCT1 transport proteins on the basolateral membrane and decreasing basolateral bicarbonate uptake capacity through decreased NBC1 protein expression. These effects decrease bicarbonate uptake capacity through NBC1 and help to offset the increased MCT1, since MCT also creates alkalotic pressure by expelling protons from the cytosol.