Figure 1.

Challenge study timeline. Triangles represent timing of deep nasopharyngeal swab collection. The first swabs were collected upon arrival to the livestock laboratory, 7 d before challenge. The second set of swabs was collected before challenge on d −1. The third set was collected at the time of the calf's first treatment, which occurred when at least 1 cm² of consolidation was observed and ≥6 h had elapsed since challenge (denoted by asterisk). The fourth set of swabs was collected following final examination on d 14, before euthanasia. US = lung ultrasound; CRS = clinical respiratory score.