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Social distancing for cattle to eradicate BVD

The ability to eradicate BVD from individual farms within two years was identified for the UK, but national eradication is a tougher task

03 September 2020, at 8:15am

The architecture of the bovine viral diarrhoea (BVD) eradication schemes in Scotland, Wales, Northern Ireland and England is strong and viable. Speaking to Professor Joe Brownlie in August 2020, he credits the discovery of BVD in 1946 as a cause of acute diarrhoea in the USA, followed by worldwide recognition of the role of the virus in respiratory disease, diarrhoea and abortion. Even at a quick glance, the RVC BVD website indicates the sheer volume of work in the UK over the past 40 years contributing to the understanding and development of an eradication programme. Some of the studies involve deep science but each study adds more knowledge and this is continuing today. The ability to eradicate BVD from individual farms within two years was identified for the UK, but national eradication is a tougher task.

The way to achieve eradication is by identifying and removing persistently infected animals (PIs). Reinfection is then prevented by vaccination, high levels of biosecurity and surveillance. It must be heart-warming to the architects of the schemes to hear veterinary surgeons say that “it is easy to test and remove, and doable to eradicate BVD”, “a no-brainer for farmers”. The aspiration in 2016 for BVDFree England was that national eradication was targeted for 2022.

When the COVID-19 restrictions on farm visits were introduced, the effort required to continue towards accreditation by the Cattle Health Certification Standards (CHeCS) was questioned as essential work. Testing of animals before turn out this year was widely missed. The next opportunity is this autumn and Jenny Hull (BCVA BVD lead) is encouraging practices to gear up for considerable activity. Veterinary practices benefitting from the £5.7 million “Stamp It Out” funding have been unable to hold cluster meetings to fulfil the initial requirement of the programme. Some use of online discussion groups has led to a resolution. It is worth noting that the funding runs until the spring of 2021. Efforts are ongoing to flow into further financial support but the activity required has changed somewhat.

As farmers engage with disease control programmes, so the task of individual farm and national eradication becomes more difficult. Within veterinary practices, identifying the clients refusing to engage will become increasingly important. It has been indicated that “the BVDFree England scheme will be run on a voluntary basis until most of the cattle industry is covered by the scheme and at that point a solid case can be presented to the government for collaboration on the introduction of compulsory measures” (Booth et al., 2016). Veterinary surgeons will have a view on the introduction of such measures that could include every calf tag and test (no passport until completed), illegal to move persistently infect-ed cattle and keeping neighbours safe.

Joe Brownlie has also made observations on the role of vaccines. “If talking about just the single BVD component of a multi-component calf respiratory vaccine, then 80 percent protection or above might be adequate to give protection. However, when considering foetal protection, the situation is quite different. The aim here is to prevent any viral particle gaining access to the placenta as, once it has infected the maternal placenta, it can ‘grow’ across the interface and infect the foetus. The bovine placenta is sufficiently thick with five layers and total integrity (no leakage) that no maternal immunity can cross to the foetus to help it in its early immune-incompetent period. Thus, it cannot influence the process of the foetal PI described above. So, the vaccine must give 100 percent protection not 80 percent, not even 99 percent!” (Brownlie, 2014).

Poor fertility, immunosuppression and an increase in secondary disease are clearly recognised with BVDV infection. Also identified is that the majority of production and economic losses within a herd are the result of subsequent acute infections of susceptible animals following contacts with a PI. The economic losses on the farm and at national level increase directly according to the percentage of PIs. A 2 percent PI prevalence records double the economic losses of a 1 percent prevalence. It is clearly stated that vaccines need to be used within a strategy that combines other control methods. With general familiarity now of the term social distancing for people, to reduce the spread of COVID-19, the social distancing of cattle is likely to be better understood. Derek Armstrong, lead veterinary science expert of the Agriculture and Horticulture Development Board (AHDB) considers that a stronger disease control mindset may lead to cattle being kept within their group bubble and greater attention given to at-risk trading.

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There does appear to be a need for a change in awareness. The 2020 BVD farmer survey carried out by Boehringer Ingelheim Animal Health highlighted strengths and weaknesses within the four national schemes. Extracting from the assessment by Matt Yarnold, too many farmers do not cull PIs immediately. However, of the farmers who had previously retained a PI, 90 percent said that they would not do so again. Their experiences include PIs that did not reach a productive size or died and animals that required extensive disease treatments. It is suggested that farmers are becoming less tolerant of neighbours who hold onto PIs. Farmers also report having slipped up with their intended vaccination schemes. Missing key dates has taken place in up to a quarter of herds, leading to gaps in protection.

It is interesting to view the veterinary surgeon presentations for the 2020 BVDZero case awards on YouTube. Paul Crawford presented the case of a herd where there were no incoming animals but which suffered a major BVD outbreak in a naïve herd. There were two major indications from this case. Many will remember that during the foot and mouth crisis nearly 20 years ago, one herd that suffered led to neighbours having their cattle shot. Despite the measures to keep the virus out, including disinfectant mats on roads, spraying of vehicles and strict biosecurity, it appeared easy for a virus to spread from farm to farm. The case outlined by Paul showed that his client had 40 other farms next to the fields that held his cattle at different times. Each of his neighbours were potential BVDV sources, with common use of personnel and some equipment. But the most striking revelation is the impact on the farmer, who also takes part in the video. It also is identified in the farmer survey that the impact of BVD is not limited to the animals; human stress is a real issue in having to deal with disease but also losing freedom from disease status.

Laura Donovan reported on the hunting down of 34 PIs on client farms, highlighting how difficult it is to get testing protocols accepted by farmers who will not be keeping the heifers. She calls for legislation or active support to enhance the attractiveness of the eradication scheme for non-engaging farmers. A common point was made by Laura and Jenny but in slightly different phrasing: Laura indicates that any programme on-farm needs to be watertight and Jenny insists that there must be no loopholes as the BVD virus will penetrate any gaps in protection. Their views and experiences are probably shared by many cattle vets.

It seems likely that the activity of veterinary surgeons and their clients, this winter and coming spring, may make or break the local and national BVD eradication programmes.

References
Author Year Title
Booth, R., MacGillivray, F., Armstrong, D. and Brownlie, J. 2016 Control of bovine viral diarrhoea virus at the national level: a brief summary of European BVD control past, present and future. Livestock, 21, 338-345
Brownlie, J. 2014 BVD — why vaccination alone is not the complete answer to eradication. Livestock, 19, 221-224

LARGE ANIMAL CORRESPONDENT

Following a 16-year apprenticeship with Beecham, Richard established a project management and development consultancy and writes regular contributions for the veterinary press.

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