Abstract #LB7P

# LB7P
Effects of increasing propionate concentration on short-term metabolism in liver explants from dairy cows in the postpartum period.
K. M. Kennedy*1, M. S. Allen1, 1Michigan State University, East Lansing, MI, USA.

Our objective was to determine the temporal effects of increasing concentrations of propionate on hepatic metabolism of dairy cows in the postpartum (PP) period. Liver of 6 dairy cows (3 primiparous: 9.00 ± 1.00 (mean ± SD) d PP and 3 multiparous: 4.67 ± 1.15 d PP) was biopsied and used in a block-design liver explant experiment. Treatments consisted of 3 concentrations of 13C3-sodium propionate at 1, 2 or 4 mM. Explants were incubated in 2 mL of supplemented medium 199 at 38°C and sampled at 0.5, 15 and 60 min. Explants were analyzed for [M + n] citrate, isocitrate, succinate, fumarate, malate, pyruvate, lactate, glutamate, and glucose by GC-MS and for acetyl CoA, propionyl CoA, succinyl CoA, and methylmalonyl CoA by LC-MS/MS. Data were analyzed with mixed models and repeated measures. Increased concentrations of 13C3-propionate increased total 13C% enrichment of propionyl CoA, succinyl CoA, succinate, fumarate, malate, and citrate over time (P ≤ 0.01). Treatment did not affect total 13C% enrichment of hepatic glucose (0.89 vs. 0.89 vs. 1.00%; P = 0.79) or acetyl CoA (4.23 vs. 4.48 vs. 4.87%; P = 0.79) but total 13C% enrichment increased over time for both (P < 0.001). Total 13C% enrichment of pyruvate (2.18 vs. 3.36 vs. 4.18%; P < 0.001) and [M+2] pyruvate (1.39 vs. 2.15 vs. 2.54%; P < 0.001) increased over time with increased concentrations of propionate. Increases in 13C% enrichment of [M+4] citrate (2.36 vs. 3.30 vs. 4.00%; P < 0.001) and [M+5] citrate (1.28 vs. 1.81 vs. 2.30%; P < 0.001) indicate propionate conversion to acetyl CoA and subsequent entry of acetyl CoA into the TCA cycle. Because these cows were in a lipolytic state, the conversion of pyruvate to acetyl CoA is inhibited. However, the relative partitioning of pyruvate to oxaloacetate or acetyl CoA is dependent upon enzyme activities. This research indicates that at least some propionate can be converted to acetyl CoA and oxidized in the TCA cycle. Metabolic reactions occur very rapidly and understanding short-term metabolism may improve feeding strategies for dairy cows in the PP period.

Key Words: propionate metabolism, liver, dairy cows