title: Effects of exposure to Bovine viral diarrhoea virus 1 on risk of bovine respiratory disease in Australian feedlot cattle.
abstract: Viruses play a key role in the complex aetiology of bovine respiratory disease (BRD). Bovine viral diarrhoea virus 1 (BVDV-1) is widespread in Australia and has been shown to contribute to BRD occurrence. As part of a prospective longitudinal study on BRD, effects of exposure to BVDV-1 on risk of BRD in Australian feedlot cattle were investigated. A total of 35,160 animals were enrolled at induction (when animals were identified and characteristics recorded), held in feedlot pens with other cattle (cohorts) and monitored for occurrence of BRD over the first 50days following induction. Biological samples collected from all animals were tested to determine which animals were persistently infected (PI) with BVDV-1. Data obtained from the Australian National Livestock Identification System database were used to determine which groups of animals that were together at the farm of origin and at 28days prior to induction (and were enrolled in the study) contained a PI animal and hence to identify animals that had probably been exposed to a PI animal prior to induction. Multi-level Bayesian logistic regression models were fitted to estimate the effects of exposure to BVDV-1 on the risk of occurrence of BRD. Although only a total of 85 study animals (0.24%) were identified as being PI with BVDV-1, BVDV-1 was detected on quantitative polymerase chain reaction in 59% of cohorts. The PI animals were at moderately increased risk of BRD (OR 1.9; 95% credible interval 1.0-3.2). Exposure to BVDV-1 in the cohort was also associated with a moderately increased risk of BRD (OR 1.7; 95% credible interval 1.1-2.5) regardless of whether or not a PI animal was identified within the cohort. Additional analyses indicated that a single quantitative real-time PCR test is useful for distinguishing PI animals from transiently infected animals. The results of the study suggest that removal of PI animals and/or vaccination, both before feedlot entry, would reduce the impact of BVDV-1 on BRD risk in cattle in Australian feedlots. Economic assessment of these strategies under Australian conditions is required.
authors.affiliation: The University of Queensland, Queensland Alliance for Agriculture and Food Innovation, St. Lucia 4072, Queensland, Australia.
authors.forename: K E
authors.initials: KE
authors.lastname: Hay
authors.affiliation: Department of Primary Industries and Fisheries, Animal Science, St. Lucia 4072, Queensland, Australia.
authors.forename: R C K
authors.initials: RC
authors.lastname: Ambrose
authors.affiliation: Jemora Pty Ltd., P.O. Box 2277, Geelong 3220, Victoria, Australia; The University of Queensland, School of Veterinary Science, Gatton 4343, Queensland, Australia.
authors.forename: J M
authors.initials: JM
authors.lastname: Morton
authors.affiliation: Department of Primary Industries and Fisheries, Animal Science, St. Lucia 4072, Queensland, Australia.
authors.forename: P F
authors.initials: PF
authors.lastname: Horwood
authors.affiliation: Department of Primary Industries and Fisheries, Animal Science, St. Lucia 4072, Queensland, Australia.
authors.forename: J L
authors.initials: JL
authors.lastname: Gravel
authors.affiliation: Department of Primary Industries and Fisheries, Animal Science, St. Lucia 4072, Queensland, Australia.
authors.forename: S
authors.initials: S
authors.lastname: Waldron
authors.affiliation: Department of Primary Industries and Fisheries, Animal Science, St. Lucia 4072, Queensland, Australia.
authors.forename: M A
authors.initials: MA
authors.lastname: Commins
authors.affiliation: Department of Primary Industries and Fisheries, Animal Science, St. Lucia 4072, Queensland, Australia.
authors.forename: E V
authors.initials: EV
authors.lastname: Fowler
authors.affiliation: The University of Queensland, Infectious Disease Epidemiology Unit, School of Population Health, Herston, Queensland 4006, Australia.
authors.forename: A C A
authors.initials: AC
authors.lastname: Clements
authors.affiliation: The University of Queensland, Queensland Alliance for Agriculture and Food Innovation, St. Lucia 4072, Queensland, Australia; The University of Queensland, School of Veterinary Science, Gatton 4343, Queensland, Australia.
authors.forename: T S
authors.initials: TS
authors.lastname: Barnes
authors.affiliation: The University of Queensland, Queensland Alliance for Agriculture and Food Innovation, St. Lucia 4072, Queensland, Australia. Electronic address: t.mahony@uq.edu.au.
authors.forename: T J
authors.initials: TJ
authors.lastname: Mahony
mesh_terms: D000821:Animal Feed / Q000821:virology; D000822:Animal Husbandry; D000818:Animals; D000914:Antibodies, Viral / Q000097:blood; D001912:Bovine Virus Diarrhea-Mucosal Disease / Q000175:diagnosis / Q000453:epidemiology* / Q000517:prevention & control / Q000635:transmission; D002417:Cattle; D015331:Cohort Studies; D030241:Diarrhea Virus 1, Bovine Viral / Q000235:genetics / Q000302:isolation & purification; D015995:Prevalence; D060888:Real-Time Polymerase Chain Reaction / Q000662:veterinary; D012307:Risk Factors; D014765:Viral Vaccines / Q000008:administration & dosage
chemical_list: D000914:Antibodies, Viral; D014765:Viral Vaccines
keywords: Bovine respiratory disease; Bovine viral diarrhoea virus 1; Feedlot cattle; Persistent infection; qPCR