Bovine Virus Diarrhoea (BVD) infection is a widespread disease of major economic importance to cattle farmers. It is caused by a virus which infects cattle and to a lesser extent sheep and other
ruminants. A recent SAC study demonstrates that up to approximately 40% of dairy and beef herds in Scotland have been exposed to BVD, and that there are 2,000 to 4,000 Persistently Infected animals in the country.
Although BVD does cause diarrhoea, the main disease occurs when BVDV infects susceptible pregnant cows in the first 4 months of pregnancy before the foetus has developed its own immune system. The virus crosses the placental barrier into the uterus and can cause foetal death and reabsorpbion, presenting as infertility or ‘repeat breeding’. Other infected foetuses die later and can be aborted right up to term or be stillborn. Many foetuses however survive to term. Some are damaged and grow poorly but many are apparently normal. All of them are persistently infected (P.I.) with the virus, which is widespread in their bodies.
The disease is mainly spread by these Persistently Infected, (or P.I.) cattle. They will have BVD all their lives and they shed virus extensively, infecting cattle around them. Most die as calves or stirks from a fatal enteritis (mucosal disease) but a few live much longer and some P.I. animals appear normal. If a P.I. cow breeds successfully she will always produce a P.I. calf. Therefore getting P.I cattle out of the national herd is critical to any eradication attempt.
When non-pregnant cattle encounter BVD infection they may suffer only a mild disease that goes undetected (transient fever, milk drop, mild scour) but it can also be associated with significant suppression of disease resistance and may contribute towards the pneumonia complex or other diseases in calves .
This aspect of the disease can be of great importance in cattle rearing systems. Bulls infected with the virus may become infertile for several months so it is important to include them in any herd vaccination program.
There are some basic steps you can follow to minimise exposure of your herd to BVD:
- Only buy cattle from farms that are CHeCS-accredited BVD-free.
- Only buy cattle at BVD-free sales at markets.
- Only buy cattle that are individually certified virus-free and vaccinated.
- Isolate any cattle you bring in, that are of unknown BVD status, from the rest of your herd and have them tested for virus. Only put them into your herd once you know they are clear.
- BVD can be spread by nose to nose contact across fences. Ensure at least 3m gaps between fences bordering your land from neighbouring farms of unknown BVD status.
- Vaccination: It is important to understand that while vaccination may lessen the infection of BVD it will not eradicate BVD, either from a herd or nationally. P.I. cattle are so highly infectious that they will continue to spread BVD even if the herd is vaccinated. It is vital that the vaccine is administered exactly as instructed on the data sheet. This means giving two doses 4-6weeks apart and then a booster 6/12 months later and annually thereafter. If you don't follow the
instructions, your herd will not be properly protected. It is possible to eradicate BVDV either with or without the use of vaccines, but if a non-vaccination route is chosen, biosecurity is critically important.
The Scottish Government has committed to supporting an industry-led scheme to eradicate BVD from Scotland. The plan is in four stages:
Stage One: Subsidised screening.
Stage One ran from September 2010 to April 2011. The Scottish Government provided £36 towards testing for BVD for each herd, and a further £72 towards further testing or veterinary advice if the result was positive.
Stage Two: Mandatory Annual Screening.
All keepers of breeding cattle herds are required to screen their herds for BVD by 1 February 2013, and annually thereafter. A range of testing methods is available. Also, where there are
calves born in non-breeding herds, they must be tested within 40 days of birth.
Stage Three: Reducing the spread of infection
Early in 2012 the Scottish Government will consult on requirements to be placed on breeding cattle herds from 1 December 2012. Proposals include:
- A ban on knowingly selling Persistently Infected cattle;
- Requiring the herd's BVD status to be declared before sale
- Movement restrictions on herds that are not free of BVD.
Stage Four: Biosecurity controls
From a date not earlier the 1 December 2013, herds that have a persistent BVD problem that goes unchecked may be required to protect their cattle neighbours through double-fencing or housing.
My result was 'not-negative'. What now?
Firstly, a not-negative result doesn't mean you definitely have BVD in your herd. It can mean that cattle in your herd have been exposed to BVD in the past and have recovered. Or it can mean that the laboratory test result was uncertain.
Until December 2012, the result you get won't impact on your ability to go about your normal business. But from 1 December 2012 there will be consequences to having a not-negative herd status.
A not-negative result means you should take action. This will involve further testing of your herd which we are can advise you on.
If you do have a BVD infection in your herd, the most important thing is to find out if you have any P.I. animals. If you do have a P.I. animal, it should be culled or sent for slaughter as quickly
as possible. P.I. cattle may enter the food chain so you will be able to get market value. The sooner you identify and remove any P.I. cattle, the sooner you will be able to achieve a 'negative' status. This will also protect your herd from further infection and poor performance.