title: Associations between animal characteristic and environmental risk factors and bovine respiratory disease in Australian feedlot cattle.
abstract: A prospective longitudinal study was conducted in a population of Australian feedlot cattle to assess associations between animal characteristic and environmental risk factors and risk of bovine respiratory disease (BRD). Animal characteristics were recorded at induction, when animals were individually identified and enrolled into study cohorts (comprising animals in a feedlot pen). Environmental risk factors included the year and season of induction, source region and feedlot region and summary variables describing weather during the first week of follow-up. In total, 35,131 animals inducted into 170 cohorts within 14 feedlots were included in statistical analyses. Causal diagrams were used to inform model building and multilevel mixed effects logistic regression models were fitted within the Bayesian framework. Breed, induction weight and season of induction were significantly and strongly associated with risk of BRD. Compared to Angus cattle, Herefords were at markedly increased risk (OR: 2.0, 95% credible interval: 1.5-2.6) and tropically adapted breeds and their crosses were at markedly reduced risk (OR: 0.5, 95% credible interval: 0.3-0.7) of developing BRD. Risk of BRD declined with increased induction weight, with cattle in the heaviest weight category (≥480kg) at moderately reduced risk compared to cattle weighing <400kg at induction (OR: 0.6, 95% credible interval: 0.5-0.7). Animals inducted into feedlots during summer (OR: 2.4, 95% credible interval: 1.4-3.8) and autumn (OR: 2.1, 95% credible interval: 1.2-3.2) were at markedly increased risk compared to animals inducted during spring. Knowledge of these risk factors may be useful in predicting BRD risk for incoming groups of cattle in Australian feedlots. This would then provide the opportunity for feedlot managers to tailor management strategies for specific subsets of animals according to predicted BRD risk.
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: The University of Queensland, School of Veterinary Science, Gatton 4343, Queensland, Australia; Jemora Pty., Ltd., PO Box 2277, Geelong 3220, Victoria, Australia.
authors.forename: J M
authors.initials: JM
authors.lastname: Morton
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
authors.affiliation: The University of Queensland, Infectious Disease Epidemiology Unit, School of Population Health, Herston 4006, Queensland, Australia; Current address: The Australian National University, College of Medicine, Biology and Environment, Research School of Population Health, Canberra 0200, Australian Capital Territory, 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
mesh_terms: D000818:Animals; D001315:Australia / Q000453:epidemiology; D001835:Body Weight; D048090:Bovine Respiratory Disease Complex / Q000453:epidemiology* / Q000209:etiology / Q000235:genetics; D002417:Cattle; D002418:Cattle Diseases / Q000453:epidemiology* / Q000209:etiology / Q000235:genetics; D004777:Environment; D008137:Longitudinal Studies; D011446:Prospective Studies; D012307:Risk Factors; D012621:Seasons
keywords: Bovine respiratory disease; Causal diagram; Feedlot; Risk factors; Total effects