The primary focus of the research was to determine the effect of porcine reproductive and respiratory syndrome virus (PRRSV) infection on the mature boar and evaluate the role of the boar in seminal transmission of PRRSV. Experimentally infected boars were evaluated for clinical signs of disease, changes in semen parameters, and duration of seminal shedding of PRRSV. Boars remained clinically healthy following challenge and no changes attributable to PRRSV infection were noted in semen parameters. Variable shedding of PRRSV in semen was observed, with boars shedding for 13, 25, 27, and 43 days after challenge;The ability of an experimental PRRSV vaccine to reduce seminal shedding of PRRSV was evaluated in 4 boars. Intramuscular administration of the PRRSV vaccine occurred 5 and 2 weeks prior to challenge. The 4 vaccinated and 3 control boars were collected twice weekly for 32 days following challenge. The control boars were still shedding at the conclusion of the experiment. Vaccination appeared to affect the duration of viremia and seminal shedding in some boars as evidenced by shedding only occurring through days 4 and 7 post-challenge in 2 of the vaccinated boars;Seminal transmission of PRRSV through artificial insemination was evaluated in gilts. Six control gilts were artificially inseminated with extended semen prior to exposure of the boar to PRRSV and 5 gilts were artificially inseminated with extended semen following exposure of the boar to PRRSV. Although PRRSV was demonstrated in the semen used to inseminate 5 gilts, a lack of seroconversion by the gilts indicated transmission did not occur. There was however, a marked difference in pregnancy rates between the 2 groups of gilts suggesting that PRRSV either prevents conception or interferes with pregnancy maintenance.