EFFECTS OF A MODIFIED-LIVE VIRUS-VACCINE AGAINST PORCINE REPRODUCTIVEAND RESPIRATORY SYNDROME IN BOARS

Objectives-To determine whether Vaccine virus is found in serum and se men of vaccinated boars, whether vaccination prevents subsequent shedd ing of wild-type virus after challenge exposure, and whether semen and blood variables are altered after vaccination or challenge exposure w ith wild-type virus, or both. Design-Throughout the 50-day postvaccina tion period, serum and semen from exposed boars were evaluated for the presence of porcine reproductive and respiratory syndrome virus (PRRS V). All boars were then challenge-exposed with PRRSV isolate VR-2332 a nd evaluated for an additional 27 days. Semen quality variables, seros tatus, and blood variables were monitored. Animals-7 PRRSV-seronegativ e adult boars. Procedure-Semen was collected 3 times weekly and evalua ted by use of a nested reverse-transcriptase polymerase chain reaction for detection of PRRSV RNA. Serum was obtained weekly and evaluated b y nested reverse-transcriptase polymerase chain reaction, virus isolat ion. and PRRSV ELISA. Semen quality variables were evaluated 3 times w eekly, and CBC was performed weekly. Results-Vaccine virus was shed in the semen of all vaccinated boars, but shedding was of shorter durati on in 4 of 5 vaccinated boars than that generally observed after expos ure to wild-type virus. After challenge exposure, shedding of wild-typ e Virus in semen was shortened or eliminated in 4 of 5 vaccinated boar s. Percentage of forward movement and normal spermatozoal morphology a nd motility were significantly reduced in vaccinated boars after chall enge exposure. Conclusions-Vaccine Virus was shed in semen of vaccinat ed boars, but vaccination generally reduced or eliminated shedding of wild-type PRRSV after challenge exposure. Semen quality appeared to be less than optimal, particularly after vaccination and subsequent chal lenge exposure with wild-type virus. Clinical Relevance-Extra-label us e of the PRRSV vaccine in boars remains controversial because some boa rs may still shed wild-type virus in semen after challenge exposure at postvaccination day 50. Semen quality also appeared to be altered aft er vaccination and subsequent challenge exposure.