Testing and management strategies for effective beef and dairy herd BVDV biosecurity programs.

Elements of a bovine viral diarrhea virus (BVDV) biosecurity program, associated costs and benefits, and criteria veterinarians and producers can use in considering whether to adopt a program are described in this report. Protection against BVDV infections includes proper immunization, identification and elimination of persistently infected (PI) carrier cattle, and prevention of exposure of cattle at risk to BVDV. The decision to implement a BVDV biosecurity program must be based on a herd-by-herd cost-benefit analysis. Costs include diagnostic testing as well as costs imposed by constraints on production practices, which are necessary to implement the program. Benefits include reduced disease loss, potential added value of replacement breeding animals which can be marketed as test-negative for PI infection, and pregnant females at low risk of carrying a PI fetus. Various herd-level diagnostic strategies have been devised to screen herds for the presence ofBVDV, identify and eliminate PI carrier cattle, or help prevent new exposure of the herd to BVDV. No universally applicable protocol exists for herd level BVDV biosecurity. The specific biosecurity methods used in each herd depend on the type of livestock production system involved. Important variables to consider are the number of animals in the herd, livestock concentration, distribution of animal groups, and desired level of biosecurity assurance. When BVDV virus is known to exist in a herd, control of new infections must take into account the possible presence of PI animals. A single PI animal can serve as the source of virus for a herd, and a stringent herd testing program may be required to identify and eliminate PI animals. Producers must understand the risks of re-exposure occurring in a BVDV-free herd and the importance of continuous management to prevent contact with cattle from other herds. In BVDV-free herds, it is essential to annually test and confirm the BVDV PI-free status of all calves born. Purchased animals should be isolated and tested before being added to the herd to avoid introduction of transiently infected animals. It is strongly recommended that bred heifers from outside sources not be added to the BVDV-free herd. Purchasing tested, non-pregnant replacement heifers is less risky than buying tested pregnant females. If tested, pregnant cattle are purchased, then the offspring must also be tested to confirm their BVDV PI-free status before introduction into the herd.