Microbiome-derived proline dipeptides underpin improved nitrogen utilization efficiency in dairy cattle.

In 30 dairy cows, proline-containing dipeptides among 349 detected small peptides are linked to higher nitrogen utilization efficiency (milk N/intake N), alongside S15 peptidyl-peptidase activity.

• Why it matters: Dairy nitrogen losses and environmental pollution are driven by low NUE, yet how rumen small peptides—an important nitrogen pool—shape nitrogen turnover is unclear.
• What they did: The study built a genome-resolved atlas of predicted small-peptide metabolism and combined isotope-labeling metabolomics with metagenomics, then used in vitro fermentation, metatranscriptomics, and targeted quantification to test proline-dipeptide accumulation and S15.001 function.
• The result: Proline-dipeptide accumulation matched transcriptional patterns for nitrogen assimilation and amino acid biosynthesis, and bacterial incubation plus heterologous expression confirmed S15.001 hydrolyzes Xaa-Pro substrates, enabling precision nutrition strategies targeting ruminal peptide metabolism.

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