Most farms are on board now with regular (3 times a year) monitoring of herd BVD antibody levels and checking for PIs (persistently infected BVD carrier) in the herd between calving and mating via the bulk milk. If you aren't doing this then discuss with one of our vets next time you see one.
BUT what about the youngstock? When heifers enter the milking herd as 2 year olds we get an opportunity to use bulk milk to check that none are PIs..... if there is a PI, a substantial amount of damage has already been done in terms of liveweight gain for youngstock, susceptibility to other diseases (e.g. yersiniosis, IBR), and reproductive effects on heifers. Perhaps it would have been better to find and remove these animals sooner? Alternatively, a PI may not even make it to the milking herd as it has either died or been culled as an empty earlier on.....but still after having some negative effects on the performance of your youngstock. There are benefits to finding and removing BVD PIs as early as practicable. There are 2 ways to go about this:
1) Individually blood test or ear notch all keeper calves at any time - commonly done at the same time as disbudding, or when coming through the yards for a drench later on.
2) Wait until calves are 10 months old (still premating) and test 15 animals from the mob - pooling their blood and checking the antibody level will give us an indication as to whether they have been exposed. If low - not likely a PI in the mob, if high - more likely to have had PI exposure so can decide then to individually test. This test doesn't work in younger animals as the BVD antibodies they got from colostrum will interfere with the test result.