Highlights:

• “Cattle carry M. haemolytica isolates with a high level of genetic diversity at arrival.
•  Genetic diversity decreases between 1 and 13 days-on-feed, with only 1 or 2 genetic clusters becoming dominant in each pen.
•  Specific clones of M. haemolytica can spread between cattle within a given pen and between pens of cattle.
•  Herd of origin was associated with genetic clusters of M. haemolytica.
•  Antimicrobial resistance genes are widespread in dominant M. haemolytica isolates collected at 13 days-on-feed.”