Effects of propionate concentration on short-term metabolism in liver explants from dairy cows in the postpartum period

Our objective was to determine the temporal effects of increasing supply of propionate on propionate metabolism in liver tissue of dairy cows in the postpartum (PP) period. A total of 6 dairy cows [primiparous: n = 3, 9.00 +/- 1.00 d PP (mean +/- SD) and multiparous: n = 3; 4.67 +/- 1.15 d PP] were biopsied for liver explants in a block-design experiment. Explants were treated with 3 concentrations of [C-13(3)]sodium propionate of 1, 2, or 4 mM. Explants were incubated in 2 mL of Medium 199 supplemented with 1% BSA, 0.6 mM oleic acid, 2 mM sodium l-lactate, 0.2 mM sodium pyruvate, and 0.5 mM l-glutamine at 38 degrees C and sampled at 0.5, 15, and 60 min. Increasing the concentration of [C-13(3)]propionate increased total C-13% enrichment of propionyl coenzyme A (CoA), succinate, fumarate, malate, and citrate with time. Concentration of propionate did not affect total 13C% enrichment of hepatic glucose or acetyl CoA, but total C-13% enrichment increased with time for hepatic glucose. The C-13 labeling from propionate was incorporated into acetyl CoA, but increased concentrations of propionate did not result in greater labeling of acetyl CoA. However, increases in C-13% enrichment of [M+4] citrate and [M+5]citrate concentrations of [C-13(3)]propionate indicate propionate conversion to acetyl CoA and subsequent entry of acetyl CoA into the tricarboxylic acid cycle in dairy cows in the PP period. This research presents evidence that despite an increase in hepatic acetyl CoA concentration and general consensus on the upregulation of gluconeogenesis of dairy cows during the PP period, carbon derived from propionate contributes to the pool of acetyl CoA, which increases as concentration of propionate increases, in addition to stimulating oxidation of acetyl CoA from other sources. Because of the hypophagic effects of propionate, but importance of propionate as a glucose precursor, a balance of propionate supply to dairy cows could lead to improvements in dry matter intake, and subsequently, health and production in dairy cows.