Characterizing the nasopharyngeal microbiome and resistome of dairy cattle with and without bovine respiratory disease.

Bovine respiratory disease (BRD) remains a significant economic challenge in dairy cattle despite extensive vaccination programs that have been developed and implemented during the last few decades. This study investigated the nasopharyngeal microbiome and resistome of dairy cattle across various life stages to understand the roles of microbial communities associated with BRD. A case-control study was conducted on three commercial dairy farms in Northern California, collecting nasopharyngeal swabs from 69 animals, including preweaned calves, weaned heifers, and lactating cows with and without BRD. Shotgun metagenomic sequencing was used to characterize both microbiome and resistome profiles observed at the time of BRD diagnosis. Results revealed that BRD is associated with distinct microbial community patterns, rather than the increased abundance of a specific pathogen. Age was a critical factor influencing microbial diversity, with adult cows showing the highest diversity and weaned heifers with BRD showing the lowest. A total of 1,164 bacterial species were identified, with BRD cases harboring 14 unique species compared to control animals. BRD cases were characterized by the co-occurrence of multiple respiratory pathogens, including