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Effects of Butyrate During Subacute Ruminal Acidosis on VFA Transport Capacity in the Rumen Epithelium of Holstein Dairy Cows
This study examined the effects of exogenous butyrate during subacute ruminal acidosis (SARA) on the membrane VFA-transport proteins in the rumen epithelium. Sixteen mid-lactation Holstein cows fed a TMR including a pelleted concentrate supplement consisting of 60 % barley grain, 20 % corn grain, and 20 % wheat grain on a dry matter basis. For 2 pre-trial days, all cows were adapted to the full amount of concentrate supplement to increase the dietary NFC to 44.0%. Cows were blocked by DIM and assigned either a butyrate treatment or control treatment for 7 days. Cows assigned the butyrate treatment were ruminally dosed twice daily with a calcium butyrate salt at 2.5% of their pre-trial DMI. Cows assigned the control treatment were ruminally dosed with a carrier. On days 1 and 7, blood, rumen fluid, and rumen biopsies were sampled for serum BHBA concentrations, VFA profiles, and transport protein abundance, respectively. Rumen pH was continuously measured on days 6 and 7 using an in-dwelling pH-measuring device. There was no difference in SARA between control and butyrate treatments (rumen pH < 5.6 for 598 ± 97 min/d vs. 536 ± 89 min/d, P = 0.65). Ruminal butyrate concentration were higher in the butyrate treatment compared to control treatment on both days 1 (9.88 vs. 22.60 ± 0.94 mM, P < 0.05) and 7 (8.60 vs. 21.60 ± 0.94; P < 0.05). Serum BHBA was also elevated in the butyrate treatment animals on day 1 (910 vs. 4201 ± 265 μM, P < 0.05) and day 7 (800 vs. 3262 ± 265 μM, P < 0.05) compared to control animals. Immunofluorescence showed an increase in the abundance of monocarboxylate co-transporter isoform 1 (MCT1), sodium/proton exchanger isoform 3 (NHE3) and sodium/bicarbonate co-transporter isoform 1 (NBC1) in all cows between days 1 and 7. By day 7, butyrate dosing increased the abundance of MCT1 (11275 ± 953 vs. 14747 ± 953 A.U., P < 0.05) and decreased the abundance of NBC1 (15065 ± 992 vs. 11122 ± 992 A.U., P< 0.05) compared to control cows. These results suggest SARA increases the capacity for proton expulsion from the cytosol as well as VFA export into the bloodstream. Butyrate increases the capacity for VFA uptake by increasing the abundance of MCT1 on the basolateral membrane and decreasing NBC1 to maintain intracellular pH.
Keywords: butyrate, epithelium, transport