Association between the level of antibodies in bulk tank milk and bovine respiratory syncytial virus exposure in the herd

Klem, T. B.; Tollersrud, T.; Østerås, O.; Stokstad, M.

Serology of young animals supported that the majority of the 11 herds with markedly increased levels of antibodies against BRSV had had a recent infection. Interestingly, in the herds with negative young stock, there was a clear age limit between negative and positive animals. The interval between the oldest negative and the youngest positive should therefore be a good indicator of time since exposure. In the two herds with no signs of recent infection, the positive animals were the oldest and they had most likely had an infection many years ago. The results showed that a BTM sample can be positive with relatively high PP values despite only one or a few positive animals contributing to the milk tank. The long duration of detectable antibodies combined with the many different factors that influence the composition of BTM makes the interpretation of positive samples as a measure of recent infection difficult.