Rumen DNA virome and its relationship with feed efficiency in dairy cows.

Background: The rumen harbors a diverse virome that interacts with other microorganisms, playing pivotal roles in modulating metabolic processes within the rumen environment. However, the characterization of rumen viruses remains incomplete, and their association with production traits, such as feed efficiency (FE), has not been documented. In this study, rumen fluid from 30 Chinese Holstein dairy cows was analyzed using next-generation sequencing (NGS) and High-Fidelity (HiFi) sequencing to elucidate the rumen DNA virome profile and uncover potential viral mechanisms influencing FE.

Results: Integrated NGS and HiFi sequencing enhanced the length, completeness, and resolution of viral operational taxonomic units (vOTUs) compared to NGS. A total of 6,922 vOTUs were identified, including 4,716 lytic and 1,961 temperate vOTUs. At the family level, lytic viruses were predominantly from Siphoviridae (30.35%) and Schitoviridae (23.93%), while temperate viruses were primarily Siphoviridae (67.21%). The study annotated 2,382 auxiliary metabolic genes (AMGs), comprising 1,752 lytic virus-associated AMGs across 51 functional categories and 589 temperate virus-associated AMGs across 29 categories. Additionally, 2,232 vOTU-host metagenome-assembled genome (hMAG) linkages were predicted, with Firmicutes_A (33.60%) and Bacteroidota (33.24%) being the most prevalent host phyla. Significant differences in viral populations were observed between high and low FE groups across multiple taxonomic levels (P < 0.05). Two pathways were proposed to explain how rumen viruses might modulate FE: (1) Lytic viruses could lyse beneficial host bacteria linked to favorable cattle phenotypes, such as vOTU1836 targeting Ruminococcaceae, resulting in diminished organic acid production and consequently lower FE; (2) AMG-mediated host metabolism modulation, exemplified by GT2 carried by vOTU0897, which may enhance Lachnospiraceae fermentation capacity, increasing organic acid production and thereby improving FE.

Conclusions: This study constructed a comprehensive rumen DNA virome profile for Holstein dairy cows, elucidating the structural and functional complexity of rumen viruses, the roles of AMGs, and vOTU-hMAG linkages. The integration of these data offers novel insights into the mechanisms by which rumen viruses may regulate nutrient utilization, potentially influencing FE in dairy cows. Video Abstract.