2014-04-14   facebooktwitterrss
Understanding Bovine Viral Diarrhoea Virus (BVDV)

Bovine Viral Diarrhoea Virus (BVDV), despite the name, doesn’t often cause diarrhoea in adult cattle! The main effects of it that we see are reduced fertility, abortions and general suppression of immunity that can lead to pneumonia, scour and other infectious disease.

“The incidence of BVD is not fully known in the UK but in recent years, the majority of farmers have become aware of the disease and most are now testing. Many are already vaccinating even if they do not fully understand the disease.” comments Pam Brown Vet at Alnorthumbria Veterinary Group’s Wooler branch.

Cattle

photo © farm-images.co.uk

Over the last 2 years, using funding from DEFRA through AHDB and XLVets (UK) Ltd, Alnorthumbria Vets co-ordinated with other local practices to deliver a BVD scheme. The key elements have been education of all farmers within the area, subsidised testing of cattle for exposure to BVD, and follow up advice on how to proceed as a co-ordinated group of connected farms.

The areas that they have covered so far are the Coquet Valley (2012), Forestburngate (2013) and from there northwards to the Scottish border on the west of the A697. For the last two years Scotland has had its own compulsory BVD testing programme meaning that all herds must test annually to find out their status, and legally they cannot knowingly sell an infected animal except direct to slaughter. It is hoped that a similar scheme will eventually be rolled out in England.

Alnorthumbria Vets have now tested 82 farms in the area. This involves blood sampling five 9-18 month old unvaccinated animals from each separately managed group (2 groups on most farms). The samples are tested for antibody to BVD which at this age, they will only have if they have been exposed to the disease and mounted an immune response. If only 1 or 2 out of 10 calves test positive, it is unlikely that there is a persistently infected (PI) animal present on the farm but they may have been exposed to the infection through poor biosecurity such as contact with neighbours’ cattle. If 4 or more out of 10 test positive, we assume that a PI is present on farm.

The confusing part is that calves that test positive for antibody are not the ones to worry about – they have been exposed to the infection but have mounted a healthy immune response. The worrying calves are those that are antibody negative; PI calves are unable to make antibodies. On farms where they were suspicious of a PI, they then tested all calves (plus adults with no calves in this group) for BVD virus, culled any that were positive and continued testing calves born on farm for the next 2 years using special ear tags that collect a sample of tissue to test.

Cattle cannot become PIs – they are born this way when the dam is infected early in pregnancy. This is why, vital to the control of BVD, is vaccination of breeding cattle before going to the bull. Of the 11 positive farms (including store buyers) it was found, only 45% were vaccinating properly. This shows that although vaccination has helped considerably in the control of this disease, it is not fool-proof. No vaccine is 100% effective and most farmers did not know their BVD status before they started vaccinating. Vaccines may get missed or are given to cattle fighting off other diseases at the time which makes them less effective.

Alnorthumbria Vets held follow up meetings with involved farmers to discuss the results and to try to encourage them to continue to test annually. The best value way to do this is by joining the Scottish Agricultural College Premium Cattle Health Scheme which involves blood sampling 5 calves from each group (as detailed above) each year. This is a good monitoring tool but BVD accreditation also commands a premium on any breeding stock that is sold.

Another major point that vets always talk about is biosecurity. Part of the scheme involved drawing maps of the farms showing where there was nose-to-nose contact with neighbours’ cattle. Some of this contact could be avoided by double-fencing, keeping pregnant animals away from these areas and so on.

The good news is that more funding has just become available so Alnorthumbria Veterinary Group now plan to extend this heavily subsidised testing and education into other areas of the Group. The details are still emerging but they will be passed on to their farmers through their newsletters in the coming months.

Alnorthumbria Vets

Related Links
link Northern Ireland BVD Eradication Programme Update
link Greater Threat from Staggers this Spring
link Can We Breed Livestock Resistant to TB?
link Calving Without Catastrophes!
link Veterinary


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