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, as they will have the virus all of their lives and spread it in huge quantities. They are born BVD Positive and remain so for the rest of their lives. Many will die within the first year of life, but some can live much longer and may appear normal. Cattle infected with BVD after birth are transiently infected and will normally recover in around four weeks, but do suffer from a reduced ability to fight other infectious disease and are likely to have impaired fertility until they recover.
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. It is best practice to remove BVD Positive animals from the herd as soon as possible. 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 purposes.
Herds that have a BVD Positive animal are BVD Positive and are restricted. Only BVD Negative animals can move out of the herd, and no animals can move in except under licence from APHA. Movement licences will only be issued in exceptional circumstances. 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.
From 18 May 2020, 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 unannounced 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.
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