The association of the rumen virome with methane emissions in dairy cattle

Enteric methane production in ruminants is a major environmental concern, yet its association with the ruminal virome remains largely unexplored. Here, we conduct a bioinformatic analysis on previously published ruminal metagenomes from 448 Holstein cows to investigate the virome and its association with methane production. We identify 8933 viral operational taxonomic units (vOTUs), including bacteriophages, archaeophages, megaviruses, and virophages. Differences between high- and low-emitting cows are observed. Low emitters show greater abundance (mean log-FC = 0.72, P_adj ≤ 0.049) of some vOTUs infecting bacteria like Prevotella, whereas greater abundance (mean log-FC = 0.70, P_adj ≤ 0.047) of archaeophages and megaviruses infecting Methanobrevibacter, ciliates, and fungi, all microorganisms linked to methane production, are observed in high emitters. Associations between viruses and microorganisms might suggest viruses influence methane emissions by modulating key microbial populations. Although mechanisms remain unclear, rumen viruses could serve as biomarkers for selecting low-emission animals or developing microbial interventions.