Because porcine circovirus-associated disease (PCVAD) has spread rapidly across North America, boar semen has been implicated as a possible source for dissemination of the virus.

To address this issue, and determine if there are differences in semen shedding of porcine circovirus type 2 (PCV2) isolates, 15, 7-month-old PCV2-negative boars were randomly allotted to three different groups. The first group served as control, the second was inoculated with PCV2a (North American-like virus) and the third group was inoculated with PCV2b (European-like virus).

Semen and serum were collected during the 90-day trial at Iowa State University (ISU).

Research concluded that PCV2a and PCV2b were both shed in low levels in semen in the two groups, of experimentally infected boars. Semen was shed for up to 12 weeks.

Overall, the amount of shedding was low and variable among individual boars within groups, and peak shedding occurred approximately three weeks post-challenge.

Detection of PCV2 in semen corresponded well with detection of PCV2 DNA in serum samples and blood swabs.

This trial verified that mature boars shed low quantities of PCV2a and PCV2b in semen, and that semen is a potential route for PCV2 transmission amongst swine herds.

In a second trial, a swine bioassay model was used to determine if PCV2-positive semen was infectious. Twelve, 4-week-old, PCV2-negative pigs were divided into four groups. All of the 4-week-old naŃ—ve pigs that were inoculated intraperitoneally (abdominal area) with PCV2-positive semen became infected with either PCV2a or PCV2b.

But when the same semen samples were extended, and used to artificially inseminate PCV2-negative gilts in a third trial, those gilts did not develop PCV2 infection, nor did they show evidence of PCV2-associated reproductive failure. All gilts inseminated with PCV2-positive semen became pregnant and carried pregnancy to term. There was no evidence that fetuses became infected with PCV2.

Researchers concluded that experimental inoculation of boars with PCV2 produces infection; however, it has yet to be determined if PCV2-positive semen is a risk for transmission and dissemination of PCVAD.

Research was funded by the Pork Checkoff.

Researcher: Tanja Opriessnig, Iowa State University. Contact Opriessnig by phone (515) 294-1950, fax (515) 294-6961 or e-mail tanjaopr@iastate.edu.