Scottish BVD Eradication Scheme: guidance

Persistently infected cattle (PIs)

Cows that get infected with BVD in their first four months of pregnancy can give birth to a persistently infected (PI) calf. These PI animals are the major source of BVD infection: they remain infected throughout their lives and spread the virus in huge quantities. They are born BVD Positive and remain so until death. Many die in the first year of life, but some can live much longer and may appear normal.  A few even reach breeding age, but if they have their own calf, it will be PI too.

Cattle infected with BVD after birth are transiently infected and will normally recover in 2 to 3 weeks, but suffer from immunosuppression (a reduced ability to fight other infectious disease) and are likely to have impaired fertility for some weeks until they recover. 

Having a PI in the herd causes transient infection in unprotected cattle, which shows up as waves of endemic disease (e.g. pneumonia, scours, ringworm) as groups of cattle catch BVD, become temporarily immunosuppressed and succumb to other infections that they would normally be able to fight off. 

If the PI is in contact with unprotected pregnant females, their unborn calves will be affected.  Worst of all, if the females are in the first four months of pregnancy, their calves will be PIs and the cycle of infection and immunosuppression will start again.

Preventing PI calf births

If completed in advance of breeding, BVD vaccination is effective in preventing a high proportion of BVD infections in dams, and therefore avoiding the birth of PI calves.  Speak to your vet for advice.

If possible, avoid grazing pregnant females in fields where there is a risk of nose-to-nose contact with cattle from other farms.   

If you show in-calf females, consider vaccinating them ahead of the show season.

What to do with PI    

All BVD Positive animals must be housed indoors, separately from BVD Negative animals or those of unknown status. To safeguard welfare, single BVD Positive animals can be housed with another animal provided that this does not give rise to any appreciable risk of spreading BVD. APHA will carry out inspections of BVD Positive herds to ensure compliance with the housing requirement. APHA have produced guidance on the standards of housing that will be required.  Read the APHA guidance and a leaflet on housing bovine viral diarrhoea positive animals.

Keepers can choose to retest a Positive animal to find out whether it is a PI or only transiently infected. The retest must be done by a vet.  If opting for a confirmatory retest, it is best to wait for 3 weeks after the first sample was taken.  This distinguishes transiently infected animals from PIs.

It is not illegal to keep the Positive animal as long as it is correctly housed, but it is best practice to remove BVD Positive animals from the holding as soon as possible. Even when housed, there is a risk of a PI spreading BVD via farm staff or equipment, and PIs usually die before they reach slaughter weight.  Those that do are slow to finish and if they produce a calf, it will also be a PI.

Removal is by culling on farm or sending the animal directly to an abattoir. BVD Positive animals are only permitted to move directly to an abattoir, they cannot be moved for any other purpose except under licence from APHA. Licences are only issued for exceptional reasons, e.g. research/teaching purposes. 

BVD Positive herds have their CPH listed on ScotEID’s PI locator, which is a biosecurity tool to alert cattle keepers to the presence of BVD in their parish. Keepers of BVD Positive animals have 40 days to retest and/or remove the animal from their herd before their CPH is listed on the PI locator.

Herds that have a BVD Positive animal are restricted.  If the Positive animal is still in the herd 40 days after the positive result was reported by the lab, all on moves are stopped.  For breeding herds, no off moves are permitted, except of BVD Negative animals or those going direct to slaughter.  Movement licences will only be issued in exceptional circumstances.