John Hoskins, Director of the NBA firmly believes that monitoring BVD with the use of tag tests has helped to make it easier to eradicate what is a very complex disease. He is keen to stress that elimination is an achievable target for all UK producers.
 
When attached the tag takes a tissue sample for analysis, it can be used on any age of animal and John currently uses it primarily on his calves to identify and remove Pl’s (Persistently Infected Animals).
 
BVD currently represents one of the biggest economic drains to the UK cattle industry resulting in reduced fertility and higher levels of pneumonia and scour in calves.  It is recommended that as part of the check, 9 to 18 month old animals should have a sample tested for BVD antibodies. At this age the animals will not have any maternal antibodies, therefore this test would highlight any positive results as a result of exposure to the virus.
 
John explains this further from his own herd perspective “Ear tag tissue testing is so much easier than blood testing as I can do it myself rather than calling on the Vet.  This really is a two minute job and tissue samples can be stored rather than sending them off straight away.  I do believe that ear tag tissue testing for BVD either using official ear tags or button tags are making it easier for farmers to eradicate this disease.”
 
A real indication that BVD is evident in the herd will be lower-than-expected pregnancy rates, abortions, birth defects, low birthweight calves, poor calf health and calf loss between birth and weaning.
A Pl (Persistently Infected Animal) remains infected with BVD throughout its entire life.  The persistent infection comes about as a result of foetal infection in the first 120 days of gestation.  Primarily this occurs if the dam herself is Pl or, if a naïve dam becomes infected with the virus in early pregnancy.  Pl calves cannot produce an immune response to combat the virus, consequently they shed virus for their entire life.
 
Compounding the issue, a Pl calf has a negative impact on all of the surrounding calves.  Even up to weaning there are indications that a Pl calf in the group will have a huge negative impact on the growth of the other calves.
 
John goes onto say: “If an antibody positive result is evident in your check list, it is a good idea to test all adult cattle for the virus rather than waiting to test the calves when they are born. It is then worth bleeding or ear tag testing the whole herd for virus in order to identify persistently infected animals and cull straight away. Detecting Pl animals and culling infected animals may be more costly in the short term but will prove hugely beneficial in the long term.”
 
There are many ways to search for a Pl animal in the herd and it is often best to start a Pl search with the calves and the young stock; however older animals within the herd can also be Pl’s and should never be overlooked.
 
Testing calves and young stock can also provide information about the BVD status of the dams from the respective calves.  Any calf testing negative for the virus in tissue would indicate it is not Pl; the dam of the calf may also be regarded as not infected as Pl dams would always produce Pl claves.  Any calves testing positive for the virus should be isolated and retested in 3 weeks, the dam should also be tested.  It is highly recommended that if a Pl is found and culled, any calves born after that date should be tagged and tested at birth for an additional 12 month period in order to establish if there has been any lasting effect from exposure to the virus.
 
Concluding, John says: “If the breeding herd is virus negative it means that there is no adult persistently infected animal, however I would strongly recommend that farmers will need to ear tag tissue test the calves just to be certain that a Pl has not been born as it is possible for a dam to test virus negative and produce a Pl calf.”