Orsel, KarinMcMullen, Christopher A.2022-03-142022-03-142020-08-12McMullen, C. A. (2020). Bacterial Respiratory Microbiota and its Role in Respiratory Health in Beef Cattle (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.http://hdl.handle.net/1880/114476Bovine respiratory disease (BRD) is one of the most significant diseases facing the North American beef industry. Mounting concern over the role mass medication with antibiotics in beef production may play in antimicrobial resistance has elevated pressure on the industry to develop novel techniques and approaches for controlling BRD. This includes approaches that involve modulation of the bovine respiratory tract microbiota. The overall aim of this thesis was to investigate the role of respiratory bacterial microbiota in respiratory health and disease in beef cattle. Four studies were designed to assess different features of the respiratory microbiota using a targeted amplicon (16S rRNA gene) sequencing approach. In the first study, the bacterial microbiotas present along the entire cattle respiratory tract were described to determine which upper respiratory tract niches may contribute the most to the composition of the lung microbiota. In the second study, evolution of the nasopharyngeal bacterial microbiota of beef calves was characterized from the time of spring processing to a targeted 40 days after arrival at the feedlot. In the third study, nasopharyngeal bacterial microbiotas of beef feedlot calves raised without the use of antimicrobials that were either healthy or diagnosed with BRD were characterized and compared. In the fourth study, the progression of the nasopharyngeal and tracheal bacterial microbiotas of beef calves during the development of BRD were described. The findings of all studies were summarized and discussed. Although the nasopharynx was confirmed to likely be the most important location that should be targeted in bovine respiratory microbiota research, it appears the role of the respiratory bacterial microbiota in cattle health and disease is more complex than originally anticipated. Indeed, no common patterns of change in community composition over time, including over large periods of time and during the development of clinical BRD, were observed. These findings may affect how we research the role of the bovine microbiota in respiratory health, as well as how we design and implement novel methods for controlling, preventing, and diagnosing BRD in beef cattle.enUniversity of Calgary graduate students retain copyright ownership and moral rights for their thesis. You may use this material in any way that is permitted by the Copyright Act or through licensing that has been assigned to the document. For uses that are not allowable under copyright legislation or licensing, you are required to seek permission.shipping feverbronchopneumoniamicrobiomenasaloropharyngealtonsillarnatural cattleantibiotic freelongitudinalcase-controlhyperthermiareticulo-rumenBiological SciencesAgriculture--Animal PathologyBiology--Veterinary Sciencedoctoral thesis10.11575/PRISM/39636