References
Managing BVDV at the herd level part 1
Abstract
Bovine viral diarrhoea virus (BVDV) is a costly disease and its eradication is the focus of the English voluntary scheme, BVDFree. The process of identifying a farm as negative or not negative is broken down into four stages using ADAM: assess disease risk; define herd status; action plan for BVD control; monitor progress. This process is based on the long-established protocols defined by Cattle Health Certification Standards. The first two stages are discussed in this article with the others following in part 2 of this series.
The risk assessment for current infection should focus on incoming animals to the herd, boundary fences and existing vaccination programmes. Suitable testing can then follow with a choice of newborn screening or youngstock cohort surveillance, with optional bulk milk analysis in dairy herds. Farms that show initial evidence of endemic BVDV infection can undertake further testing to discover the source.
Bovine viral diarrhoea virus (BVDV) is a common virus of cattle subject to compulsory eradication schemes in many countries, including Scotland and Ireland. Estimated to cost the UK cattle industry £25–61 million pounds annually, it is the most costly single-agent infectious disease (Bennett, 2003). This is because of its rapid spread within the herd, production losses (particularly due to its impact on fertility) and induction of immunosuppression increasing incidence of other diseases (calf scour, respiratory disease, mastitis, lameness, infertility) (Evans et al, 2019). For more detail on the economic impact of BVDV, the reader is referred to the systematic review by Yarnall and Thrusfield (2017).
The primary source of the virus is a calf born persistently in-fected (PI) with BVDV (PI calf). They are tolerised to the virus in utero, and produce virus throughout life, in all body secretions. PI calves can die young, but one third of them may survive longer than 2 years (Booth and Brownlie, 2012), and enter into the breeding herd. PI calves are produced when a naïve dam is infected for the first time before 125 days of pregnancy.
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