BVD virus can be excreted in semen due to persistent infection, acute infection, persistent testicular infection and prolonged testicular infection. Virus can be transmitted to susceptible cows via cryopreserved semen. Therefore, if semen is not processed under Certified Semen Services guidelines (which results in CSS being stamped on the straw), it should be tested by PCR to validate the absence of virus prior to use, suggest Dr. Dan Givens, Auburn University. While localized testicular infections are of some concern, persistent and acute infections of bulls are the most common causes of contaminated semen. Until transmission is demonstrated from bulls that develop this condition after initial exposure to PI animals or vaccination with a noncytopathic modified-live vaccine, the focus should be prudent vaccination and standard testing of bulls.
After other standard tests have failed to detect the source of BVDV on a farm, semen should be tested using a validated PCR assay. Routine screening of semen from bulls that test negative on standard assays is not currently recommended. If semen is not cryopreserved using CSS guidelines, a straw should be assayed using a validated PCR test to ensure the absence of BVDV prior to use. Givens adds that adequate vaccination of bulls with a cytopathic modified-live vaccine will prevent prolonged testicular infection. “Bulls need to be vaccinated appropriately.”
Source: Drovers.com