Multi-omics study links rumen and hindgut microbiome and metabolome to feed efficiency in Holstein calves (microbiomejournal.biomedcentral.com)

• Integrated metagenomics and metabolomics revealed distinct rumen and fecal microbiomes in high-efficiency (low RFI) vs low-efficiency (high RFI) calves.
• High-efficiency calves showed enhanced starch/protein digestibility and propionate fermentation, with key species Erysipelotrichaceae_bacterium and Hungatella_sp.
• Serum glutamate was elevated in high-efficiency calves despite lower intake; glutamate supplementation in mice improved nitrogen metabolism and gut barrier.

"A multi-omics study integrating metagenomics and metabolomics of 20 Holstein female calves identified distinct microbial and metabolic signatures associated with feed efficiency measured by residual feed intake (RFI). High-efficiency (low RFI) calves exhibited enhanced starch and protein digestibility, propionate-oriented fermentation, and elevated serum glutamate despite lower intake. Glutamate supplementation in mice improved nitrogen metabolism and gut barrier function, suggesting a central role for glutamate metabolism in feed efficiency."