BVD - what do you need to do about it on your farm?
BVD ( Bovine Virus Diarrhoea) virus is widespread in the UK cattle population with evidence of 90% of cattle herds having been exposed to it. Just because it is widespread does not mean that we have to accept its presence, however. Eradication schemes in European countries like Norway and now closer to home in Orkney, Norfolk, Suffolk (and getting off the ground in Somerset) are demonstrating massive improvements in herd health and profitability when the virus is controlled and then eradicated.
How do I know the virus is present on my farm?
Two of the most common ways in which evidence of the virus is detected on a farm are screening of bulk milk samples for BVD antibody when your vet is concerned about general herd health and fertility and testing blood samples from cows which have aborted. If the virus is circulating there may be poor calf health with increased levels of scours and pneumonia. Blood samples and in the worst cases post-mortem tissue samples from affected calves may demonstrate the presence of virus. The virus is most commonly spread by persistently infected (PI) animals.
So I know I’ve got it – surely the answer is just to vaccinate, isn’t it?
Once you know that there is evidence of BVD virus in your herd, it’s important to sit down with your vet and decide on a course of action to deal with the infection. A number of factors will influence the plans you make. One positive bulk milk test for antibody provides a starting point but some more lab tests may be necessary to help the planning process. A newly available PCR test which can detect BVD virus in a bulk milk sample is extremely useful. A positive result proves that there is at least one PI cow whose milk is going into the tank.
Examples of virus control programmes
In a “flying herd” with a bull running with the cows where BVD virus might be causing infertility, abortions and the birth of weak calves, immediate whole adult herd vaccination is likely to be the strategy. This will protect the cows against infection from any PI animal in the herd. Bulls can be PI animals so it’s sensible to make sure he’s not a carrier by getting a blood sample checked for virus. Don’t forget to vaccinate the bulls and to adhere to manufacturer’s instructions on dose intervals, boosters and routes of administration. As the vaccination takes effect and immunity to the virus develops then you should see benefits. Improved calf health for cross bred calves going to market or being sold as potential suckler cow replacements is highly significant at today’s calf prices.
For long term control and eradication of the virus in a herd the strategy will be more ambitious and inevitably harder work than a simple vaccination programme – but results should justify the effort, especially in a closed herd with home reared replacements.
Identifying and culling PI animals at the same time as providing protection to vulnerable cattle by vaccinating is a realistic plan for both individual farms and the national herd. Screening batches of young stock for PI animals is getting easier and cheaper with the availability of PCR testing on blood and even calf skin ear notch samples!
Regular bulk milk testing on my farm always yields negative results for BVD exposure –what should I do?
It is important to keep monitoring the situation- quarterly bulk milk testing for antibody as a minimum. Keep disease out-don’t buy in stock or allow your animals to come into contact with anyone else’s without considering the risks of BVD virus. Talk to your vet about pre-purchase screening and other biosecurity precautions.