Abstract. The prevalence of organisms known to be associated with bovine respiratory disease (BRD) was investigated in cattle prior to export. A quantitative reverse transcription polymerase chain reaction assay was used to detect nucleic acids from the following viruses and bacteria in nasal swab samples: Bovine coronavirus (BoCV; Betacoronavirus 1), Bovine herpesvirus 1 (BoHV-1), Bovine viral diarrhea virus 1 (BVDV-1), Bovine respiratory syncytial virus (BRSV), Bovine parainfluenza virus 3 (BPIV-3), Histophilus somni, Mycoplasma bovis, Mannheimia haemolytica, and Pasteurella multocida. Between 2010 and 2012, nasal swabs were collected from 1,484 apparently healthy cattle destined for export to the Middle East and Russian Federation. In addition, whole blood samples from 334 animals were tested for antibodies to BoHV-1, BRSV, BVDV-1, and BPIV-3 using enzyme-linked immunosorbent assay. The nasal prevalence of BoCV at the individual animal level was 40.1%. The nasal and seroprevalence of BoHV-1, BRSV, BVDV-1, and BPIV-3 was 1.0% and 39%, 1.2% and 46%, 3.0% and 56%, and 1.4% and 87%, respectively. The nasal prevalence of H. somni, M. bovis, M. haemolytica, and P. multocida was 42%, 4.8%, 13.4%, and 26%, respectively. Significant differences in nasal and seroprevalence were detected between groups of animals from different geographical locations. The results of the current study provide baseline data on the prevalence of organisms associated with BRD in Australian live export cattle in the preassembly period. This data could be used to develop strategies for BRD prevention and control prior to loading. Nasal shedding and seroprevalence of BRD in live export cattle 7 Export of Livestock, Standard 3, http://www.agriculture.gov. au/biosecurity/export/live-animals/advisory-notices/2011/ export_advisory_notice_2011-01). Time in the assembly depot allows the animals to recover from road transport, acclimatize to shipboard rations, and receive any health checks or treatments required by the importing country. However, comingling, handling, and sorting of animals that have been recently transported from multiple farms also provides an ideal environment for transmission of viruses and bacteria between animals in the assembly depot.Viruses implicated in the pathogenesis of BRD include Bovine herpesvirus 1 (BoHV-1), Bovine respiratory syncytial virus (BRSV), Bovine viral diarrhea virus 1 (BVDV-1), Bovine parainfluenza virus 3 (BPIV-3), Bovine coronavirus (BoCV), bovine rhinoviruses, and bovine adenoviruses. Bovine rhinoviruses and adenoviruses probably have only a minimal role in the pathogenesis of BRD, while BoHV-1, BPIV-3, and BRSV are recognized as primary respiratory pathogens, and BVDV-1 as a significant predisposing pathogen (reviewed in previous publications 20,52 ). Since its first isolation in association with respiratory disease in 1993, 67 BoCV has received attention as an emerging BRD pathogen, and is now thought to make a substantial contribution to the development of BRD in feedlot cattle.
59,65Mannheimia haemo...