Byline: Iain Carrington
BOVINE Viral Diarrhoea (BVD) virus is widespread in the national herd with many farms showing evidence of infection, although vaccination is more common now than it was 10 years ago.
This virus is responsible for bovine viral diarrhoea, mucosal disease, poor conception and early embryonic death, foetal mummies, the birth of brain-damaged calves, eye defects in newborn calves and a lower resistance to other diseases. With this list of problems associated with the disease you would think it would be easy to diagnose. Well, unfortunately this is not always the case! Often other diseases cloud the picture, and although you often know the disease is present on a farm it is difficult to quantify the effect and the cost. Bulk milk testing on dairy farms or blood testing on beef farms have proven effective in demonstrating the presence of infection and probable persistently infected animals.
These persistently infected cattle are responsible for 27% of the loss attributed to this disease. Many of these animals are poor doers and will probably contract mucosal disease and die, but it is now known that some appear normal while excreting virus all their lives.
These animals represent a major source of infection within and between herds.
The most effective animals to blood test are home-bred heifers between nine and 15 months of age because if there is infection present they will show immunity in their blood.
Although this is complicated as persistently infected animals also show no immunity! BVD is the most important worldwide viral disease of bovines, in many other countries where eradication programmes are in place. …