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.

Population-level effects of risk factors for bovine respiratory disease in Australian feedlot cattle

“…The Australian National Bovine Respiratory Disease Initiative was a prospective longitudinal study in cattle in medium-sized to large Australian feedlot cattle that identified and quantified the effects of numerous putative risk factors for BRD (Hay et al, 2014;Hay et al, 2016a;Hay et al, 2016b;Hay et al, 2016c;Hay et al, 2016d;Hay et al, 2016e). The current study extends these findings.…”

“…These collapsed variables were used in the current study to simplify analyses and to ensure there were at least modest numbers of animals in each category. Exposure to 'BVDV in the cohort' (yes, no) was a cohort-level variable which categorised cohorts as exposed if any animal(s) had tested positive to Bovine viral diarrhoea virus 1 (BVDV-1) on qPCR testing (Hay et al, 2016a). The number of study animals in the animal's group-13 ('group-13N') essentially reflected the size of the animal's group of cattle over an extended period as the majority of group-13s had been stable (i.e.…”

“…The causal pathways depicting relationships between variables of interest and between each of those variables and the development of BRD were hypothesised a priori as previously reported (Hay et al, 2014;Hay et al, 2016a;Hay et al, 2016b;Hay et al, 2016c;Hay et al, 2016d;Hay et al, 2016e). For some variables, the total effect was considered to be of main interest, whilst for others the direct effect was more relevant.…”

Manejo do complexo respiratório bovino em confinamento: Revisão

“…Os Estados Unidos da América estimam uma perda anual com a afecção de aproximadamente U$ 1 bilhão, devido à queda produtiva, aumento de despesas com manejo, custos com medicamentos e morte dos animais (Hay et al, 2016a).…”

“…O papel da BVD (Bovine Viral Diarrhea) na patogênese do CRB é certo como doença primária e pode facilitar a colonização de agentes patogênicos nos pulmões, cuja maior exposição ao vírus demonstra maior risco da infecção no complexo respiratório em confinamentos (Hay et al, 2016a). Hay et al (2016b) demonstraram em um estudo que animais não vacinados para BVD têm o risco de desenvolver problemas respiratórios multifatoriais aumentados.…”