Understanding How BRD and AMR are Transmitted Among Feedlot Cattle

Project Title

Understanding Contagious Transmission Informs Best Management Practices for Respiratory Disease in Feedlot Calves by Leveraging Whole Genome Sequencing of a Unique Isolate Collection


Emily Snyder and Cheryl Waldner (Western College of Veterinary Medicine, University of Saskatchewan) e.snyder@usask.ca

Status Project Code
In progress. Results expected in December, 2023 ANH.02.21


Cattle always carry BRD organisms in the respiratory tract, but the “good” bacteria and the animal’s immune system normally keep them in check. When animals get stressed, the “good” bacteria and the immune system get weakened, the BRD bacteria take over, and the animal gets sick. Antibiotics are used to treat BRD, and this selects for antimicrobial resistant bacteria. Some of these BRD bacteria may also spread contagiously from animal to animal. These researchers want to clarify whether BRD and AMR arise independently in each animal, whether it’s due to spread between animals, or the degree to which they each play a role.


  • To better understand the degree to which BRD and AMR arise in individual calves, vs. the degree to which BRD and AMR spread contagiously from calf-to-calf.  

What they will do

This project will use deep nasopharyngeal swabs that have already been collected from 800 auction mart calves (from a presort sale) and penned next to each other at the LFCE (8 pens x 100 calves representing between 30 to 70 different herds per pen). Sampled were collected on arrival, and 2 and 5 weeks after arrival. The main BRD pathogens (Mannheimia, Pasteurella, Histophilus, Mycoplasma) were isolated and antibiotic resistance patterns assessed.

In this study they will determine the whole genome sequences of a subset of the Mannheimia bacteria. Very similar or identical gene sequences in bacteria from different animals (or different pens) will suggest contagious spread of BRD or AMR from animal-to-animal. Wide genetic diversity among bacteria isolated from different animals or different pens will suggest that respiratory disease and/or AMR may be arising independently in many different animals.


If BRD and AMR spread contagiously, then pre-arrival vaccination, preconditioning, filling pens as quickly as possible, and potential modifications to fencing and waterbowls may help limit the spread. If BRD and AMR are arising in individual calves, then specific antibiotic management strategies may be more important.