Table 12.

Pairwise comparisons from the repeated measures, multilevel logistic regression models for the likelihood of a calf within a pen having P. multocida with tetracycline resistance or spectinomycin resistance (antimicrobial resistance (AMR)) across time points for each year and metaphylaxis option, reported as population-averaged odds ratios (ORs) and 95% confidence intervals (CIs), accounting for clustering at the pen level. n = 1595 calves for which susceptibility data were available.

AMR Outcome of Interest	Year/Metaphylaxis	DOF Comparison	OR	95% CI	p-Value
Tetracycline	2020/tulathromycin	13DOF vs. 1DOF	0.4	0.2, 0.7	0.001
		36DOF vs. 1DOF	1.1	0.4, 2.7	0.83
		36DOF vs. 13DOF	2.9	1, 8.2	0.052
	2021/tulathromycin *	13DOF vs. 1DOF **	0.3	0, 1.7	0.25
		36DOF vs. 1DOF **	0.9	0, 5.8	0.91
		36DOF vs. 13DOF	·	·	·
	2021/oxytetracycline	13DOF vs. 1DOF	5.1	2.8, 9.3	≤0.001
		36DOF vs. 1DOF	6.0	2.9, 12.6	≤0.001
		36DOF vs. 13DOF	1.2	0.7, 1.9	0.50
Spectinomycin	2020/tulathromycin	13DOF vs. 1DOF	0.41	0.2, 0.7	0.001
		36DOF vs. 1DOF	1.02	0.4, 2.6	0.97
		36DOF vs. 13DOF	2.5	0.9, 6.9	0.084
	2021/tulathromycin *	13DOF vs. 1DOF **	0.1	0, 0.8	0.06
		36DOF vs. 1DOF **	0.5	0, 2.8	0.54
		36DOF vs. 13DOF	·	·	·
	2021/oxytetracycline	13DOF vs. 1DOF	4.3	2.5, 7.5	≤0.001
		36DOF vs. 1DOF	4.3	2.2, 8.3	≤0.001
		36DOF vs. 13DOF	1.0	0.6, 1.6	0.97

* Exact logistic regression equation performed. · odds ratio (OR) was not estimable. ** Indicates a median unbiased estimate.