Research Summary - 2
Understanding contagious transmission of Pasteurella multocida in feedlot calves by leveraging whole genome sequencing of a unique isolate collection
| Date/Time: |
9/12/2025
16:15
|
| Author: |
Emily R Snyder |
| Clinic: |
University of Saskatchewan WCVM |
| City, State, ZIP: |
Saskatoon, SK S7N 5B4 |
Emily R. Snyder, DVM, MFAM, PhD
1
;
Cheryl L. Waldner, DVM, PhD, FCAHS
1
;
1Western College of Veterinary Medicine Large Animal Clinical Sciences, University of Saskatchewan, Saskatoon, SK, S7V0N7, Canada
Introduction:
The goal of this project is to evaluate the contagious spread of Pasteurella multocida (Pm) within one pen of cattle by utilizing whole genome sequencing to identify the genetic relationships between individual isolates collected from deep-nasopharyngeal swabs at arrival and later in the feeding period. Our hope is that this research will help to inform best management practices for the control of bovine respiratory disease. A simple approach to answer these questions is to utilize whole-genome sequencing technology to identify genetic relationships between isolates collected from feedlot cattle over multiple timepoints. By conducting phylogenetic analysis of the isolates, we can identify which strains are present in a group of cattle, and if there are any shifts in the genetic population over time toward one dominant strain or another. It can also tell us to what strains cattle are entering a feedlot with and give us hints into possible common sources of exposure for cattle from disparate herds of origin.
Materials and methods:
In the fall of 2020, 100 calves were purchased from pre-sort sales through a local auction mart and placed in a research pen at a university owned feedlot in central Saskatchewan. Calves were processed and vaccinated according to industry standards and received a metaphylactic dose of the antimicrobial tulathromycin at arrival. Deep nasopharyngeal swabs were collected at two timepoints; arrival, and 13 on feed (DOF). The swabs were cultured for Pm and submitted for Illumina whole genome sequencing. A total of 57 individual Pm isolates were identified. Genetic analysis was performed on the isolates to understand how they were related to each other and to identify resistance genes.
Results:
On arrival (1 DOF), 44 of 100 calves were shedding Pm, and the genetic analysis showed a high level of genetic diversity amongst the isolates. The isolates were divided between 29 different genetic clusters, with most clusters only containing one genetically distinct isolate. On day 13, only 13 of 100 calves were shedding Pm. These 13 isolates were divided between 10 different clusters, with most clusters again only containing one isolate. All but one genetic cluster at the second timepoint was also present at arrival. Furthermore, most calves positive for Pm at both timepoints shed isolates belonging to the same cluster at both sampling times. There were also 4 calves that were only positive for Pm at 13 DOF, and one calf that “switched” clusters between the two timepoints. Strong evidence for contagious spread was not observed.
Significance:
This study described population shifts in the genetics of Pm between two sampling points: 1 DOF and 13 DOF, within a single pen of feedlot cattle. We observed a high degree of diversity in Pm isolates at arrival. In contrast to what has been observed with Mannheimia haemolytica in a previous study by our group, we did not observe an increase in shedding or a shift to one dominant genetic clone. Rather, we observed a decrease in shedding from 1 to 13 DOF. These data suggest that the shedding dynamics of Mannheimia haemolytica and Pm were quite different in these cattle. More work is needed to identify if this pattern holds true for a wider range of Pm isolates, particularly those harboring resistance genes and integrative conjugative elements.
