Proline dipeptides in the rumen linked to higher nitrogen use efficiency in 30 dairy cows

A research team reported in Nature Communications a genome-resolved map of small-peptide metabolism in the rumen microbiome. They combined chemical isotope-labeling metabolomics with metagenomics in 30 dairy cows. Among 349 detected small peptides, proline-containing dipeptides were associated with higher nitrogen utilization efficiency (NUE), together with an S15 peptidyl-peptidase that generates Xaa–Pro dipeptides. nature.comNature Communicationsnature.comOpen source ↗

Why nitrogen use matters in dairy

NUE is the share of dietary nitrogen recovered in milk (milk N/intake N). Reported values vary among individual cows from about 14% to 45%. Livestock systems account for roughly one-third of global anthropogenic nitrogen emissions, and the ruminant supply chain contributes 71% of that (about 46 Tg N per year), according to the cited estimate.

In the rumen, 60–80% of dietary protein is degraded into peptides and amino acids. Peptide-bound nitrogen makes up about half of total ruminal nitrogen. When breakdown exceeds microbial needs, ammonia is absorbed, converted to urea and mostly excreted in urine, which lowers NUE.

Peptidases in rumen genomes

The map is based on the Bovine Gastro Microbial Genome Map. Of 5978 high-quality metagenome-assembled genomes (MAGs), 3731 (62.4%) encoded peptidases annotated for small-peptide degradation, and 64.6% of these carried a single such gene. nature.comNature Communicationsnature.comOpen source ↗ Another 1820 MAGs encoded peptidyl-peptidases with a predicted role in generating small peptides; 72.3% of them carried two or more such genes.

Degradation capacity was assigned mainly to Bacteroidota (45.5%) and Bacillota_A (38.4%), while generation capacity was 96% Bacteroidota. Signal-peptide prediction showed that 76% of the generating peptidyl-peptidases carry a signal peptide, whereas 98% of the degrading peptidases lack one.

Experimental checks

In vitro rumen fermentation, metatranscriptomics and targeted quantification showed that proline-dipeptide accumulation coincided with transcriptional patterns consistent with nitrogen assimilation and amino acid biosynthesis. Bacterial incubation and heterologous expression confirmed that the S15.001 peptidase hydrolyzed Xaa–Pro substrates.

The authors describe this as a microbial proline-dipeptide axis associated with NUE and as a basis for precision nutrition that targets ruminal peptide metabolism. The data are associations from 30 cows plus laboratory experiments; feeding interventions were not tested in this work. nature.comNature Communicationsnature.comOpen source ↗