Hepatic metabolism of propionate relative to meals for cows in the postpartum period

摘要

The objective of this research was to identify potentialshort-term metabolic bottlenecks of propionatemetabolism in the liver of dairy cows in the postpartum(PP) period and how such bottlenecks are affected byfeeding status. Propionate, produced primarily fromthe fermentation of starch, decreases dry matter intakefor cows in the postpartum period, likely by stimulatingoxidation of acetyl-CoA in the liver. In this study,8 dairy cows [2 blocks of 4 cows each, 6.63 ± 1.19(mean ± SD) days PP; body condition score of 2.84± 0.39] were administered a pulse dose of either 1.5mol/500 mL of propionic acid (PA) or 500 mL of water(control; CON) to the rumen either 1 h before or 2 hafter feeding in a 4 × 4 Latin square design with a 2× 2 factorial arrangement of treatments. Liver tissuewas sampled at −1, 10 and 20 min relative to dosing,and blood was sampled at −30, −20, −10, −1, 5,10, 15, 20, 25, 30, and 60 min relative to dosing. Wehypothesized that rapid propionate absorption resultsin bottlenecks as enzymes become saturated and cofactorsrequire regeneration. The PA treatment increasedplasma propionate and insulin concentrations rapidly,with peaks reached by 5 min regardless of feeding statusand cleared from the plasma within 30 min of dosing.The PA treatment decreased plasma nonesterifiedfatty acid concentration over 30 min compared withCON before but not after feeding. The PA treatmentdecreased plasma β-hydroxybutyrate concentration andincreased plasma lactate concentration compared withCON both before and after feeding. The PA treatmentalso increased hepatic pyruvate and lactate concentrationscompared with CON. The PA treatment tendedto increase hepatic isocitrate and fumarate concentrationsbut did not affect hepatic malate and oxaloacetateconcentrations, suggesting that elevated mitochondrialNADH/NAD+ may have slowed the isocitrate dehydrogenaseand fumarase reactions. The PA treatmentalso increased succinate concentration compared withCON, suggesting that a bottleneck may be present atsuccinate dehydrogenase. The PA treatment tended toincrease citrate concentration despite having no effectson acetyl-CoA or oxaloacetate concentrations. Theseresults are in agreement with our hypothesis that rapidabsorption of propionate from the rumen and extractionby the liver results in metabolic bottlenecks in theliver that may affect feeding behavior and dry matterintake in dairy cows in the PP period.