TABLE 1.

Characteristics of each longitudinal study; the number of isolates screened using antimicrobial susceptibility testing (AST), percentage of multidrug-resistant (MDR) isolates detected, and number of isolates from each study used for subsequent analyses.

	Surveillance study 1	Surveillance study 2	Surveillance study 3	Total
Year(s) study was performed	2011–2012	2014–2015	2015–2016	–
No. of feedlots sampleda
Canada	10	17	12	31
United States	2	0	0	2
No. animals sampled in the study	68	528	159	755
No. of isolates recovered
M. haemolytica	55	238	35	408
P. multocida	8	85	34	140
Percentage of isolates found to be MDRb (No. of strains screened with AST)
M. haemolytica	67.3 (55)	55 (238)	81.8 (33)	–
P. multocida	50 (8)	70.5 (85)	90.9 (33)	–
No. of MDR isolates included in this analysis
M. haemolytica	40	80	27	147
P. multocida	6	34	30	70
Total	46	114	57	217

^aValues include feedlots where MDR strains were recovered. Only three feedlots were represented in more than one study, both sampled in study 2 and study 3 (Supplementary Table S1).^bMDR = an isolate expressing resistance to ≥3 antimicrobial classes.