Assessing recoveries of branched-chain volatile fatty acids or amino acids in dual-flow continuous cultures limited in rumen-degraded protein without or with supplemental leucine.

Authors

A F White, C Lee, K E Mitchell, A R Sanders, M E Cordonnier, M T Socha, D H Kleinschmit, J L Firkins

Published in

Journal of dairy science. Aug 25, 2026. Epub Aug 25, 2026.

Abstract

Ruminal bacteria can either synthesize branched-chain amino acids (BCAA) from central metabolites or from reductive carboxylation and transamination of the branched-chain volatile fatty acids (BCVFA). There is bidirectional mixing within a metabolic pair (i.e., isoleucine/2-methylbutyrate, leucine/isovalerate, and valine/isobutyrate). The keto acid of valine is the intermediate in its synthesis but also branches off in the leucine synthesis pathway. Therefore, we hypothesized that interconversion of ¹³C-isobutyrate with its keto acid could label both valine and, to a lesser extent, leucine, especially if increased leucine concentration inhibited its de novo synthesis from pyruvate. In Experiment 1, treatments with inadequate (8.5% formulated using NASEM, 2021) RDP and 1.72 mmol per day of each of the 3 BCVFA without or with supplemental leucine (5.16 mmol/d) were arranged in a truncated 6 × 6 Latin square design using a dual flow continuous culture system that allowed measurement of BCVFA production and recovery of isotope. Each of 3 periods consisted of 7 d adaptation that were followed by a 7-d sampling period that included 2 pulse doses of individually ¹³C-labeled BCVFA or BCAA with 4 d of washout between each dose of isotope within a respective metabolic pair. Supplemental leucine did not change degradation of nutrients or flows of bacterial N, but supplemental leucine did increase isovalerate, valerate, and caproate production. More ¹³C was recovered in bacterial protein when the isotope was dosed as a labeled BCAA than as BCVFA. Negligible ¹³C was recovered in amino acids other than BCAA, suggesting minimal metabolism beyond BCVFA. Recovery of ¹³C into branched-chain fatty acids documented the importance of branched-chain vinyl ethers in plasmalogens, which was especially important for 2-methylbutyrate. In a second experiment using starch (from potato) or cellulose (from corn) grown in ¹³CO₂, low RDP increased de novo synthesis of most amino acids from cellulose, whereas de novo synthesis of leucine increased from starch more than from cellulose. Results are discussed to further document the relative sinks of BCAA and BCVFA in bacterial cell constituents, documenting their importance in the rumen.

PMID:
42641873
Bibliographic data and abstract were imported from PubMed on 26 Aug 2026.

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