It is generally accepted that as bovine respiratory disease (BRD) develops, bacterial pathogens first proliferate in the nasopharynx and then colonize the lungs, leading to bronchopneumonia. However, such temporal changes have never been definitively demonstrated. Therefore, the objective was to describe the progression of the nasopharyngeal and tracheal bacterial microbiotas of feedlot cattle during development of BRD. Nasopharyngeal swabs and tracheal wash samples were collected from 24 heifers over 20 d after arrival at a feedlot. Heifers were assessed daily and sampled based on reticulo-rumen/rectal temperatures and development of clinical signs of BRD. The study end point for each heifer was either at BRD treatment (BRD group; n = 15) or day 20 if the heifer remained healthy or did not meet BRD treatment criteria (TOL group; n = 9). Total DNA was extracted from each sample and the 16S rRNA gene (V3-V4) sequenced. Alpha and beta diversity were compared between BRD-TOL groups and sampling locations over time. There were no common patterns of change over time in composition or diversity of either the nasopharyngeal or tracheal bacterial microbiotas of cattle that developed BRD. Health status affected bacterial composition (R² = 0.043; < 0.001), though this effect was low compared to variation among individual animals (R² = 0.335; < 0.001) and effects of days on feed (R² = 0.082; < 0.001). Specific bacterial taxa (Moraxella and Mycoplasma dispar) nevertheless appeared to have a potential role in respiratory health.

人们普遍认为，随着牛呼吸道疾病（BRD）的发展，细菌病原体首先在鼻咽中增殖，然后在肺中定植，导致支气管肺炎。然而，从未明确地证明这种时间变化。因此，目的是描述在BRD发育过程中育肥牛的鼻咽和气管细菌菌群的进程。到达饲养场20天后，从24个小母牛那里收集鼻咽拭子和气管清洗样品。每天对小母牛进行评估，并根据网状瘤胃/直肠温度和BRD的临床体征发展对其进行采样。每个小母牛的研究终点为BRD治疗（BRD组； n = 15）；如果小母牛保持健康或未达到BRD治疗标准，则为第20天（TOL组； n = 9）。从每个样品中提取总DNA，并对16S rRNA基因（V3-V4）进行测序。随时间推移，比较了BRD-TOL组和采样位置之间的alpha和beta多样性。BRD牛的鼻咽或气管细菌菌群的组成或多样性没有随时间变化的常见模式。健康状况影响细菌组成（R² = 0.043；<0.001），尽管与个别动物之间的变化相比（R ² = 0.335; <0.001）和天数对饲料的影响（R ² = 0.082; <0.001）而言，这种影响较低。然而，特定的细菌类群（莫拉氏菌和支原体）似乎在呼吸系统健康中具有潜在作用。