Despite growing concern surrounding antimicrobial use (AMU) and the importance of cow–calf herds to the Canadian livestock industry, surveillance of AMU in cow–calf herds to inform antimicrobial stewardship programs has been sporadic. Producers from the Canadian Cow–Calf Surveillance Network (87%, 146/168) provided data and almost all reported AMU in at least one animal (99%, 145/146 herds) in 2019–2020. The most common reasons for AMU were treatment of respiratory disease in nursing calves in 78% of herds and neonatal diarrhea in 67% of herds, as well as for lameness in cows in 83% of herds. However, most herds treated 30% of nursing calves from one herd. Similarly, while 56% of herds used macrolides at least once, within-herd use was the highest in nursing calves where 30% of animals. Herds using artificial insemination and calving in the winter were more likely (p = 0.05) to treat >5% of nursing calves for respiratory disease, suggesting the importance of vaccination programs for herds at risk. Overall, AMU was similar to previous Canadian studies; however, the percentage of herds using macrolides had increased from a comparable study in 2014.

The change in bacterial recovery and phenotypic antimicrobial susceptibility of 3 important bovine respiratory disease bacteria (Mannheimia haemolytica, Pasteurella multocida, and Histophilus somni) between arrival and 90 to 120 days was observed in 295 healthy fall-placed feedlot calves in western Canada using deep nasal swabs. At the arrival sampling, 28%, 28%, and 9% of calves were culture positive for Mannheimia haemolytica, Pasteurella multocida, and Histophilus somni, respectively; these rates changed to 23%, 14%, and 16%, respectively, in the post-arrival period. A decrease in antimicrobial susceptibility was observed between the arrival and post-arrival sample periods, with numerically fewer pan-susceptible isolates and little change in multi-drug resistant isolates. Between the 2 sampling periods, statistically significant decreases in susceptibility to tilmicosin and tulathromycin were observed for Mannheimia haemolytica and tildipirosin for Pasteurella multocida isolates. Results of this study suggest that changes to both the proportions of bacteria isolated and the antimicrobial susceptibility of isolates occur between arrival and ~90 days post-arrival.

Timely, accurate, and reliable laboratory tools are important for antimicrobial stewardship (AMS) in food animal production. The objectives of this study were to (1) identify factors that influence live animal respiratory sample collection for laboratory testing and (2) describe the potential for integration of laboratory testing of samples from live animals into an AMS strategy for bovine respiratory disease (BRD) management in Canadian feedlots. Utilizing focused ethnography, virtual key informant interviews were conducted with eight feedlot veterinarians from Alberta, Ontario, and Saskatchewan, Canada. Thematic analysis revealed four themes: (1) lived experience of feedlot veterinarians with laboratory testing for BRD pathogens and antimicrobial resistance (AMR), (2) evidence-informed BRD management that integrates multiple data sources and their components, (3) organizational factors that affect the uptake and use of laboratory tests, and (4) the role of laboratory testing to support AMS in BRD management. While sample collection and laboratory testing are commonly used for BRD and AMR research and surveillance, they are not routinely applied in everyday BRD management. Veterinarians identified key challenges with laboratory testing, including turnaround time, the need for clear benefits, practical implementation, and effective communication with feedlot managers. Laboratory testing must provide valuable, actionable insights to encourage its adoption in Canadian feedlot operations. If successful, such testing could support AMS and be used to justify antimicrobial use if this were to become a regulatory or market requirement.